St Helena Secondary College

Year 10 Science – Physics

Glossary

*acceleration A measure of how quickly the velocity of an object is changing. It can be positive (speeding up) or negative (slowing down).

*action In physics, one of a pair of forces. The reaction force acts in the opposite direction.

*collision When two or more objects come into contact with each other.

deceleration Another term for negative acceleration.free-body diagram A simplified diagram of an object showing all the forces

acting upon it and the size and direction of those forces.*gradient A measurement of the steepness of the slope of a graph. The

steeper the graph, the higher the gradient.*magnitude A measure of how big something is.*momentum A quantity describing the movement of an object. Calculated

by multiplying the mass by the velocity.*reaction In physics, one of a pair of forces. This acts in the opposite

direction to the action force.reaction time The time between when you see or hear something and

when you react.*resistance In physics, a force that acts in the opposite direction of

motion. Friction is an example of a resistance force.*resultant force The total force that results from two or more forces acting on

a single object. It is found by adding the forces together, taking into account their direction.

risk How likely something unfortunate is to happen.*speed A measure of the distance an object travels in a given time.

Usually measured in metres per second (m/s).*stopping distance The distance a car travels between when the driver sees

something and when the car stops. Found by adding thinking distance and braking distance.

*terminal velocity A constant, maximum velocity reached by falling objects. This happens when the weight downwards is equal to the air resistance upwards.

*vector A quantity that has a size and a direction. Force and velocity are examples of vectors. Speed, mass andvolume are not vectors.

*velocity The speed of an object in a particular direction.Usually measured in metres per second (m/s).

*weight The force pulling an object downwards. It depends upon the mass of the object and the strength of gravity.

YR 10 PHYSICS – ACT. 1 – MEASURING SPEED

Aim: To calculate the speed of various objects in motion.

Materials: Stop Watch, Measuring Wheel, Football, Tennis balls, Soccer Balls.

Procedure: 1. Record the time for each task below to travel a measured distance. 2. Calculate the speed for each in m/s and convert to km/h. 3. Complete the question on the back of the sheet.

Results:Speeds

Task DistanceTrial

1Trial

2 Avg. m/s km/h

WalkJogRun

Kick Football

Tennis ball throw

Soccer Ball

Q. To convert from m/s to km/hr simply multiply by 3.6. Explain why below.

Discussion:

Conclusion:

Conversion Questions!!!

Convert the following length units into the units specified:

a) 50 km = _______ m = ________cm

b) ______km = _________m = 10cm = _________mm

c) 12km = _________mm

d) 2.3m = _________cm = __________mm

e) 62.7 km = __________m

f) _______km = 43m

g) 4km = ________mm

Convert the following time units into the units specified:

h) 2.5h = ________min = __________s = ___________ms

i) 43min = __________ms

j) 1.2h = __________s

k) 1h = ___________min = ___________s = ____________ms

l) ________h = ___________min = 1200s = ___________ms

m) 3.4h = _______________ms

n) ________h = 1 230 000ms

Convert the following speed units into the units specified:

o) 23 km/h = ___________ m/s

p) 120000 m/s = _____________km/h

q) 10000 m/s = ____________km/h

r) 12m/s = ______________km/h

s) 1.7 m/s = ___________ km/h

t) 12.2 km/h = __________ m/s

u) 120km/h = ____________m/s

Goldie Goldfish, a speed swimmer, loves to race around the park’s pond, which is 0.5 miles around. If she can swim 20 laps around the track in 2 hours, what is her average speed?

It takes Stu, a slimy slug, 20 minutes to travel from his favorite bush to the local rubbish bin (a trip of 30 meters), how far can he travel in 1 hour (60 minutes)?

At exactly 2:00 pm, Speedy the Snail crawls onto a meter stick at the 10 cm mark. If he reaches the 65 cm mark at exactly 2:10 pm, what is his speed?

Andrew and Michael decide to have a race. Andrew knows that he is faster than Michael, so he says that he’ll take a longer route to the finish line. Instead of going straight from point A to C, he goes via point B on the way. Michael takes the direct, as shown on the diagram below:

Michael takes 5 seconds to reach point C. Andrew takes 6.2 seconds. What is:

a) Michael’s speed?

b) Michael’s velocity? (Don’t forget to include direction)

c) Andrew’s speed?

d) Andrew’s velocity?

Questions: Solve the following problems. Show all your work and remember to include the correct units.

Average distanceSpeed = time

1. A student practicing for a track meet ran 250 m in 30 sec. a. What was her average speed?

b. If on the following day she ran 300 m in 30 sec, by how much did her speed increase?

2. A car travelled 1025 km from Queensland to Victoria in 13.5 hr. What was its average velocity?

3. How fast was a plane flaying if it travelled 400 km in 30 min?

4. A student walks 10 blocks to a computer store (Assume all the blocks are equal length.) a. How long will it take him to reach the computer store if he walks 3 blocks in 2 min?

b. What is his average speed?

5. If the average speed a car is 45 km/hr, how far can it travel in 40 min?

6. The speed of light is 3 X 108 m/sec. How long does it take light to travel the 149 X 109 m distance from the sun to the Earth?

F H FHVelocity of a trolley F

You are going to carry out an experiment to calculate the velocity of a trolley. The formula forcalculating velocity is:

velocity = displacement time

MethodApparatusramp trolleywooden blocks or booksG-clampticker tape and timer scissorsglue

A Set up the ramp as shown in the diagram.

TICKER-TAPE TIMER TICKER TAPE TROLLEY

RAMP BLOCK TO STOP TROLLEY

G-CLAMP

B Clamp a block to the bench at the bottom of the ramp.

C Pass the end of the ticker tape through the ticker-tape timer and fasten it to the trolley. Check that the ticker tape can run freely.

D Switch on the ticker-tape timer.

E Let the trolley go down the ramp. Catch the trolley as it reaches the end of the ramp.

F Tear off the ticker tape where it comes out of the ticker-tape timer.

Sheet 1 of 2

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F H

P2.9 1a M9.1c

Velocity of a trolley (continued)

Results1 Draw lines on the ticker tape every 5 dots, as shown in the diagram.

1 2 3

2 Number each section of tape using consecutive numbers. DO THIS BEFORE YOU CUT UP THE TAPE.

3 Cut up the ticker tape along the lines you have drawn on it.

4 Draw axes on graph paper. Stick the sections of ticker tape next to each other on the axes, as shown on the diagram.

5 Draw a smooth line to join the top of the centre of each strip of ticker tape.

STICK THE FIRST STRIP OFTICKER TAPE DOWN SO THAT IT IS TOUCHING THE VERTICAL AXIS

STICK THE SECOND STRIP OF TICKER TAPE DOWN SO THAT IT IS TOUCHING THE FIRST STRIP

Evaluation1 The ticker-tape timer puts a dot on the tape every 0.02 seconds. What length of time does each

strip of ticker tape represent?2 The length of the ticker-tape strip represents the distance travelled in a fixed time. What is this

quantity known as?3 Work out this quantity for each strip.4 a What type of graph does the ticker tape represent?

b Label the axes appropriately. Sheet 2 of 2

272 GCSE Additional Science Copymaster File P2.9 1a © Edexcel Limited 2007

M9.1b

Extension Questions:Finding the acceleration.The acceleration of the trolley can be determined from the graph. The steepness of the graph, that is the gradient of the graph, gives the acceleration.

How do we find the gradient:a. Select two points, A and B, on the graph some distance apart,b. For these two points, read off their values on the axes as A: (SA, TA) and B: (SB, TB)c. The gradient can be found from (SB – SA) / (TB – TA)

1. Calculate the acceleration of the trolley as it rolled down the slope.

____________________________________________________________________

____________________________________________________________________

Finding the Distance travelled from the GraphThe distance travelled can be obtained from the graph. The area under the graph gives the distance travelled.

How do we find the area under the grapha. Divide the shape of the area under the graph into a triangle and a square,b. Work out the areas of the triangle and the squarec. Add the two areas together.

2. Calculate the total distance travelled by your trolley using the area under the graph.

3. Another way of determining the distance travelled is to add up all the lengths of all the strips of paper.

Determine the distance by this method.

4. How do your two answers compare?

5. Calculate the average speed of the cart. (Total distance travelled / total time taken). Your answer will

be in cm/s.

A quick word

Work out which word is meant by each of the clues and fit it into the word puzzle.

1 Distance/time (5)

2 Displacement/time (8)

3 Speed x time (8)

4 Distance/speed (4)

5 Distance in a certain direction (12)

6 A quantity with size and direction (6)

7 Another word for ‘size’ (9)

8 A vector has magnitude and ____ (9)

9 _______ velocity = displacement/time (7)

10 Not a vector (6)

Questions for: Speed and velocity1 (a)A student travels 28 metres in 4 seconds. What is the average speed?

(b) A student travels at 40 m/s for 3 seconds. What distance is travelled?

(c) A student travels at 12 m/s for 60 metres. How long does it take?

2 (a) Explain the difference between velocity and speed.

(b) Is velocity or speed a vector quantity?

(c) If a student rides around a 1600 metre roller coaster track in 200 seconds before returning to the start, what is (i) the average speed (ii) the average velocity?

3 A student on a bicycle takes 6 seconds to reach a velocity of 10 m/s from rest and then keeps this speed up for a further 20 seconds before applying the brakes for 10 seconds to stop the bicycle. (a) Draw a velocity time graph for the journey.

(b) Calculate the total distance travelled by adding up the areas under the graph (Hint: area of triangle = half base times height).

4 A train travels between two stations and its velocity is plotted on the graph below. Describe the journey in as much detail as possible.

5 25

20

40

velocity in m/s

0

0

30 50 60

Time in minutes

Acceleration, Mass and Force

Acceleration is any change in velocity, which may be a change in speed, such as from 10m/s to 20m/s, or a change in direction, such as from north to east.

All acceleration requires a force. Bigger forces produce bigger acceleration, just as two people pushing a car will be more effective than one person pushing a car (ie, more force!).Mass obviously affects acceleration also. Mass is the amount of matter of an object. It never changes unless you take away or add weight to it.

Newton’s Second Law says:Something will happen if a force is applied:

the object will accelerate and the acceleration will depend on the mass of the object.

This can be written as:Force = mass X acceleration

OR F = ma

It can also be arranged to give:

F F m= a and a= m

Balancing Forces

There is usually more than one force acting on an object. Some of these forces may balance each other out by canceling each other out. If cancellation is complete, then the overall force is zero and there will be no acceleration. You will not speed up, or slow down- you will either stay stationary or keep traveling, as you were before.

M9.3i

Velocity–time graphs and acceleration 1 F

Name Class Date 1 Draw lines to match the graphs to the correct statements about the motion shown on the graph.

a V b Vconstant

deceleration

stationary

T Tc V constant speed d V

constant acceleration

T T2 Draw lines to match the graphs to the correct statements about the motion shown on the graph.

a V (M/S) b V (M/S)

stationary

c V (M/S)

constant speed of 2 m/s

T S

constant speed of 4 m/s

T Sd V (M/S)

constant acceleration of 2 m/s2

e V (M/S) T Sconstant acceleration of 4 m/s2

T Sf V (M/S)

constant deceleration of 4 m/s2

T S T S3 Calculate the following accelerations.

a A car accelerates from rest to 50 m/s in 5 seconds.

b A plane flying at a steady speed of 100 m/s accelerates to 150 m/s in 10 seconds.

c At a set of traffic lights, a lorry slows down from 30 m/s to 0 m/s in 20 seconds.

d A cyclist travelling at a steady speed of 20 m/s decelerates to 5 m/s in 3 seconds when thebrakes are applied.

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Activity : Types of Forces Inflate a balloon, Tie a piece of light string to the knot of the balloon, Attach a small paper clip to the end of the string, Rub the balloon with a cloth to charge it up, clothing can be used, Place the balloon against a surface where it will stay put, e.g. another student, the ceiling, a

window, a wall. Now bring up a magnet to the paper clip to draw the clip to the side.

There are many types of forces acting in this arrangement.

Your task: To put on the diagram as many of these forces as you can think of.

But first, how do we put a force on a diagram?Use an arrow Where you put the tail of the arrow tells you where the force acts,

The arrow’s direction tells us which way the force is acting,The length of the arrow tells us how big the force is.

Label the arrow Every force is one object acting on another, so we can write the weight of the paper clip as Force by Earth on Paper Clip or Fby Earth on Clip.

F By Earth On Clip

All the forces in this diagram can be grouped by the type of force.Put into the space below any examples you have of the following:

Types of ForceExamples

ElectrostaticMagneticGravitationalContactTension

Force and acceleration 1 F

Name Class Date

1 For each scenario, draw a free-body diagram to show the forces acting.

The first one has been done for you.

a A bag of shopping weighs

50 N. It is picked up with a force of 60 N.

60N UPWARDS

b A girl kicks a ball. Her foot pushes forward with 18 N. Friction pushes backward with 3 N.

c A moving skateboarder drags her foot on the ground making a force of friction.

50NDOWNWARDS

d A fish swims against acurrent. The current has a backwards force of 8 N. The fish’s tail pushes forward with a force of 8 N.

e A boy is sitting on a chair reading a book. The boy’s weight is 600 N.

f A boy strikes a pool ballwith a cue. The force from the cue is 20 N. The force of friction from the table is 4 N.

2 For each of the scenarios in question 2, say what the direction of the resultant force is and whatthe effect on the object will be.

a

b

c

d

e

f

3 Which object will accelerate faster? Explain your answer.

FORCE: 80NMASS: 0.43 KG

FORCE: 80NMASS: 0.058 KG

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M9.4c

Mass and acceleration 1 F

Name Class Date

Remember: force = mass × acceleration

1 For each of the following diagrams:

● calculate the resultant force

● give the direction of the resultant force

● calculate the acceleration of the object.

a b c

2 KG 0.2KG 5N 10N 2N 5N 3N 4KG

2N

resultant force

direction

acceleration

d

resultant force

direction

acceleration

e

resultant force

direction

acceleration

f

7N 2N 10N

10KG 2.5KG 10KG0N 100N

4N 3N 1N

resultant force

direction

acceleration

resultant force

direction

acceleration

resultant force

direction

acceleration

2 Complete the table below by calculating the missing values.

Object Force (N) Mass (kg) Acceleration (m/s2)sprinter 80 2

charging elephant 1000 1000

Formula One car 500 9

cyclist 150 1.5

bullet 80 0.002

hockey ball 4 30

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Questions for: Acceleration1 (a) If a student increases velocity by 30 m/s in 5 s, what is the acceleration?

(b) If a student accelerates at 8 m/s2 for 10 s, what is the increase in velocity?

(c) If a student increases speed by 50 m/s at an acceleration of 2 m/s2, how long does it take?

2 A car travelling at 25 m/s increases its speed to 35 m/s in 5 seconds.(a) What is its acceleration?

(b) What would its acceleration be if it took 10 seconds to change speed?

3 From the graph of its velocity below, calculate the acceleration/deceleration of a bicycle during each of the periods A, B, and C.

4

8

12

5 10 15time in seconds

velo

city

in m

etre

s/se

cond

A B C

4 A fighter aircraft dives towards the ground at 100 m/s and pulls out of the dive to fly upwards again at 50 m/s. If the turn takes 3 seconds, what acceleration does the pilot feel?

5 A roller coaster travelling at 15 m/s speeds up with an acceleration of 5 m/s2 to 35 m/s; how many seconds does it take?

Data analysis – Acceleration (Extended Prac Report)1. Identify possible errors in the experimental method.

2. Explain why the last reading was not able to be recorded.

3. Suggest another method for measuring the speed of the trolley and identify advantages and disadvantages to this method.

4. Explain how consistent the results of the experiment are with Newton’s second law.

5. Predict the speed of a trolley being accelerated by the 1.0N force after 5 seconds.

6. Explain what would happen to the acceleration of the trolley if the accelerating force was kept the same but the mass of the trolley was increased.

ForcesMotion is affected by forces.

Resistance Forces: The forces that push against the direction of movement, including air resistance and the force of friction acting on the wheels that are not turned by the motor. Friction is the force resulting from the movement of one surface over another. It is very much greater when the brakes are applied. When the car is moving at a constant speed on a straight road, the thrust and resistance forces are in balance.

Upwards push of the road: On a horizontal road this force is equal in size to the weight. If the weight and upwards push of the road were not in balance, this car would accelerate downwards through the road or upwards into the air.

Weight: The force applied to the car by the Earth due to gravitational attraction. At the Earth’s surface, this force is 9.8 newtons for each kilogram of mass.

Thrust: The force applied to the driving wheels of the car by the road. (The driving wheels are the wheels, usually either the front or back wheels, that are turned by the motor) The motor turns the wheels so that they push back on the road. As a result, the road pushes forward on the wheels. When the driver turns the steering wheel, the direction of this thrust force changes, allowing the bus to turn.

M9.6a

Location, location, locationYou have met the equation

weight = mass x gravitational acceleration

This can be written W = mg where W is weight in Newtons, m is mass in kilograms and g is the gravitational acceleration.

‘g’ can also be referred to as gravitational field strength and given the units Newtons per kilogram (N/kg)

This table shows how gravitational acceleration g is different on different planets and on the Moon.

Planet Value of ‘g’ (m/s2) Weight of cup of water (N)

Mercury 3.7 (= 0.38 ge)Venus 8.8 (= 0.90 ge)Earth 9.8 (= 1ge)Moon 1.6 (= 0.16 ge)Mars 3.7 (= 0.38 ge)Jupiter 23.1 (= 2.36 ge)Saturn 9.0 (= 0.92 ge)Uranus 8.6 (= 0.88 ge)Neptune 11.0 (=1.12 ge)Pluto 0.6 (=0.06 ge)

Fill one plastic cup with water.

Suspend it (carefully) from a newtonmeter to find its weight on Earth.

Write this value in the table.

Keep this cup as it is with the water in it.

Use the values from the middle column of the table to write down what this weight would be in three other places in the solar system.

Now use your other plastic cup.

Using stones (for higher gravity) or low-density packing material (for lower gravity) and some water, make a cup which is the same weight as the value in the table for one of the other places you have chosen. Feel how this compares to your original cup.

Change the contents of your cup to model the weight in the two other places you have chosen, compare with your original cup each time.

Calculate the weights for the remaining places in the solar system to complete the table.

Describe some of the difficulties you would expect if you were living and working in a place of:

a lower gravity

b higher gravity.

Questions for: Force and acceleration1 The acceleration of an aeroplane on a runway is proportional to the net force produced by its engines.

(a) Explain what the terms in italics mean.

(b) Suppose that the acceleration of the aircraft is 25 m/s2, what would it be if the force were doubled?

2 Using F = ma at the theme park.a) A roller coaster car of mass 2 000 kg must be given an acceleration of 25 m/s2. What force is needed?

b) A different ride has an acceleration of 20 m/s2 and a force of 40 000 N. What is the total mass of the vehicle and riders?

c) If a force of 1 200 N acts on a 60 kg person what acceleration will the person be given?

3 A 2 tonne (2 000 kg) car accelerates from rest to 56 m/s in 8 seconds. What force must be exerted on the car to achieve this?

4 The graph below shows how the velocity of a motorcycle varies during a short journey. The mass of the motorcycle is 250 kg.

(a) What force accelerates the motorcycle?

(b) What force is exerted by its brakes?

5 (a) A forward force of 500 N acts on a 20 kg rock travelling forwards at 10 m/s. What is its velocity after 2 seconds?

(b) What would the velocity have been after 2 seconds if the 500 N forward force had been acting on a 20 kg rock travelling backwards at 10 m/s?

5 10 15time in seconds

velo

city

in m

etre

s/se

cond

10

20

30

Questions for Mass and acceleration1 It is sometimes possible to ‘bump start’ a car by pushing it until it is going fast enough to turn the engine

over. Explain, using the words ‘mass’, ‘acceleration’ ‘force’, why it is more difficult to get a car moving than to get a supermarket trolley moving.

2 A 2 tonne (2 000 kg) van can accelerate at 6 m/s2 when unloaded. (a) If the driver loads another tonne (1000 kg) of kit into the back, what acceleration can it now achieve?

(b) What if only 500 kg of kit had been put in?

3 A 40 kg cannon ball hits a 20 kg cannon ball that is at rest and decelerates at 50 m/s2. If the force on the 20 kg cannon ball is the same but in the opposite direction then what is its acceleration?

4 If a ship of 24 000 tonnes (24 million kg) travelling at 10 m/s with her engines off takes 20 minutes (1200 seconds) to stop in the water, what is the average drag force from the water during that time?

5 (a) A rocket has a motor that gives it a forward force of 200 N. When the fully fuelled rocket is launched horizontally it has an initial acceleration of 40 m/s2. What is the mass of the fully fuelled rocket?

(b) Extension — Rocket ScienceBy the time the rocket is just about to run out of fuel its acceleration is 200 m/s2. What mass of fuel did it burn?

Kinetic and Potential Energy

Learning Goal:

Students will explore the interaction between Kinetic and Potential energy and be able to explain the relationship when compared to a real-world example.

Materials:

Work with your lab partner sharing a computer with the following simulations:

http://phet.colorado.edu/simulations/sims.php?sim=Energy_Skate_Parkhttp://phet.colorado.edu/simulations/sims.php?sim=Pendulum_Labhttp://phet.colorado.edu/simulations/sims.php?sim=Lunar_Lander

Activity:

Begin at the Energy Skate Park site.

Part 1: Play! Build a skate ramp and choose a skater to test it. Draw a diagram of what happened to your skater on the first try:

Adjust your ramp (if needed) to keep the skater from flying off and dying! Draw a second diagram of your solution:

What variable(s) did you change? Why did it help the skater survive?

Define the following:

Kinetic Energy –

Potential Energy –

Part 2: Observe Click on the Pie Chart box and run your skater through the track again. Use this tool to help you label the spots on the ramp where there is the greatest KE and PE from Part 1. Draw your results below:

Compare what happens to KE and PE as the skater moves along the track. What general statement can you make about the relationship between KE and PE?

Now, go to the Pendulum Lab site.

Part 3: Compare

Click on the “1” button

Change the speed of the pendulum to slow it down

Click and drag the pendulum to start the motion.

Watch the KE and PE bars as the pendulum swings back and forth.

Explain (in words or with a drawing) what you see happening with the KE and PE:

How does this relate to the skater?

Extension:

Now, Go to the Lunar Lander Site.

Use the Lunar Lander to explain how KE and PE are interacting as you try to land on the target. Include a diagram and written explanation to support your theory:

Diagram Explanation

Roller Coaster Animation (Kinetic & Potential Energy)http://www.teachersdomain.org/asset/mck05_int_rollercoaster/

1) At the point 1 – Explain the break down between potential and kinetic energy?

2) At the point 2 – Explain the break down between potential and kinetic energy?

3) Between point 3 & point 4 is the potential energy increasing or decreasing?

The roller coaster weighs a total of 900 kg. 4) At Point 5 the velocity is 16m/s – Assume the potential energy is zero. Determine the Kinetic energy?

5) At point 4 the velocity is 4 m/s. Determine the kinetic energy at this point?

6) Using the kinetic energy found in question (4) for the total energy of the system. Assuming no energy is converted to heat, what is the potential energy at the top of the loop.

Using the information from the previous question, and that PE = mx g x h. What is the height of the loop.

Questions for: Falling through the air1 As a cyclist moves faster the air resistance increases steadily and the resultant force decreases until terminal

velocity is achieved. Explain what the terms in italics mean.

2 A parachutist whose mass (including all equipment) is 100 kg jumps out of an aircraft.(a) What is the parachutist’s weight?

(b) Draw a free-body force diagram of the parachutist at a time before terminal velocity is achieved. Label the forces and a possible size of the upward force.

(c) What is the upward force on the parachutist when falling at terminal velocity?

(d) Draw another free-body diagram of the parachutist at a time just after the parachute has opened and give a possible value for the upward force.

3 The forward force on a racing car as it accelerates out of a bend in a racing track is 30 000 N. The air resistance is 6 000 N. The car has a mass of 600 kg.(a) What is the resultant force on the car?

(b) What is its acceleration?

4 A search and rescue helicopter winches a casualty from the deck of a yacht. The tension in the winch cable is 750 N and the mass of the casualty is 70 kg.(a) What is the weight of the casualty?

(b) What is the resultant force on the casualty?

(c) What is the acceleration of the casualty?5 Extension — Rocket Science

A rocket with mass 8 000 kg lifts off with an initial upward acceleration of 15 m/s2.(a) What is the weight of the rocket?

(b) What is the net force on the rocket?

(c) What is the force provided by the rocket engine?

M9.4b

Collisions The concept of momentum is very useful in working out what will happen in collisions.

This is because momentum is conserved: there is the same total amount of momentum after the collision as there was before.

Here is an example.

Michael rolls a large marble, mass 50 g (0.05 kg) at a speed of 0.5 m/s. The large marble hits a stationary smaller marble, mass 20 g, which moves off at a speed of 0.25 m/s in the original direction of travel.

Before the collision After the collision

What is the momentum of the large marble before the collision?

What is the momentum of the small marble before the collision?

What is the total momentum before the collision?

What is the total momentum after the collision?

What is the momentum of the small marble after the collision?

What is the momentum of the large marble after the collision?

What is the speed of the large marble after the collision?

Is momentum a vector quantity or a scalar quantity? How do you know?

50 g20

0.5 m/s? m/s

50 g20

0.25 m/s

How would you distinguish between momentum values in opposite directions?

This time the small marble is rolled at the stationary large marble at 0.5 m/s. It collides and bounces back at 0.25 m/s.

a What is the momentum of the small marble before the collision?

b What is its momentum after the collision?

c What will be the momentum of the large marble after the collision?

d What will be the velocity of the large marble after the collision?

Questions for: How much motion?1 If all the objects mentioned below are travelling at 12 m/s what is the momentum of each?

(a) A go-cart of mass 50 kg

(b) A ship of mass 3 000 tonnes (3 000 000 kg)

(c) A ball bearing of mass 0.020 kg

2 (a) What is the velocity of a train of mass 4 000 tonnes (4 000 000 kg) if its momentum is 80 000 000 kg m/s?

(b) What would be the velocity of a 200 kg meteor with the same momentum?

3 A truck of mass 10 tonnes is travelling along a road at 8 m/s. (a) How fast would a 2 tonne car go for the same momentum?

(b) How fast would a 80 tonne sailing boat go if it had the same momentum?

4 (a) A railway truck of mass 40 tonnes has a velocity of 8 m/s. What is its momentum?

(b) If the railway truck collides and couples with another truck of the same mass and they move on together with a velocity of 4 m/s then what is their total momentum?

5 (a) A small boat has a momentum of 600 kg m/s. If the boat is moving at 3 m/s then what is its mass?

(b) If the same boat is stopped next to a quay (not secured) and a person with mass 100 kg running at 6 m/s jumps into it then what will be the total momentum of the person and the boat?

(c) What is the total mass of the person and boat now?

(d) What will be the initial speed of the boat?

Reaction Time

Aim: To measure reaction time and to investigate factors that affect reaction time.

Materials: Foot pedal (on/off switch), electric timer, power pack, red and green light board, switch and connecting wires.

Method: 1. Set up the apparatus as shown in the picture above, follow the colour coded leads. The power supplyshould be set on 10 volts DC.

2. Three students must work together to obtain results, one will be the driver, the other the operator and the third the distractor.

3. The driver sits on a chair with their foot flat on the thong.4. The switch will be turned OFF and the green light will be on. The timer must be set to ZERO. The

operator flicks the switch ON, this turns the red stop light on and simultaneously starts the timer. 5. The moment the driver notices the red light he/she applies the brake. The brake should only be applied

once and the foot kept on the pedal. To prevent the timer starting again the operator should flick the switch off. Record the time shown on the stop watch in the table

6. Repeat the process above three times, record the results in a table and then average the results.7. Repeat this experiment, but this time the distractor will distract the driver.

Results

Name of DriverActivity Trial 1 (s) Trial 2 (s) Trial 3 (s) Average (s)

ConcentratingDistracted

Discussion1. Why do you think that we take the average of three trials for each activity?2. How do the results for the distracted driver compare with the results from the concentrating driver?3. What other factors besides distractions may affect the reaction time? Are there any laws to regulate these?4. Describe an example from your own experience to show how the reaction time of a distracted driver was

affected.

ConclusionWrite a suitable conclusion.

Activity: Testing your Reflexes with a Metre RulerProcedurea. Student A holds the metre ruler as shown in the diagram. Student B holds the thumb and forefinger on

either side of the ruler at the zero centimetre mark. Do not touch the ruler. b. Without warning, student A lets go the ruler, allowing it to fall. Student B should then grasp the ruler

as fast as possible. c. Measure how far the metre ruler has dropped using the scale on the ruler. Repeat the experiment 3

times and average the results.d. From the graph below, record the time taken for you to react to the ruler being dropped in the table.

This time taken is called your Reaction Time, the time lag between the event occurring and your brain and muscles responding.

e. Now, try the experiment again, this time with the student reading a book, talking to another student, with your hand flat on the bench, and recalling some information like the names of the seven dwarfs. Record the time taken in the table below.

Trial Conditions Distance Travelled (cm) Average Time takenLooking at rulerReading a book

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50

20

40

60

80

100

120

Reaction Time (sec)

Rul

er D

ista

nce

(cm

)

Reaction times are important when driving because they contribute to the distance required to stop a car in an emergency. The driver needs to react to the emergency, place his or her foot on the brake, then have the car slow and eventually stop.

Stopping Distance = Reaction Distance + Braking Distance1. Many factors, including those of the car, road and the condition of the driver come into play here.

What physical road/car factors may affect the stopping distance?

2. What factors would affect the reaction time of the driver?

3. If you were travelling along in a car at 80 kph (22 m/s), how far would you travel before you put your foot on the brake in an emergency?(This is calculated by multiplying your best reaction time by the speed in m/s).

1. 4. On a dry road with good tyres, at 80 kph, it takes 38m to stop. What would be the total distance

travelled before the car stops?

5. Now calculate the stopping distance using your slowest reaction time.

6. How much difference is there between your best and worst results?

7. What implications do these results have in an emergency on the road?

M9.8d

Braking distance: the effect of road surface1 On a short ramp mark a starting point on the ramp (e.g. about 50 cm from the end).

2 Support one end of the ramp so that it slopes.

3 Let a trolley roll down the ramp and get a measurement for how far it travels before it stops. Write this in the table below under ‘Braking distance’.

Surface Braking distance (cm)Normal dry floor

4 Decide on four ways in which you could change the surface to change the braking distance. Write the surfaces in the table.

5 Repeat the experiment with the other surfaces until the table is complete.

6 Write down what you have found out about the effect of the surface on braking distance.

7 Explain your results in terms of friction.

8 Were your results what you expected?

The truth about stopping distances

Questions for: Thinking, braking, stopping

1 Explain the meanings of the following terms in as much detail as you can: reaction time, thinking distance, braking distance, stopping distance.

2 A rally car driver sees a fallen tree on the track ahead. It takes 0.8 seconds to react to it, but the car is travelling at 40 m/s. How far does the car travel before the driver does anything about avoiding the tree?

3 A person loads a van with half a tonne of equipment and sets off to work. It is raining and he has not had enough sleep. After five minutes of driving, a dog runs into the road ahead of him, and he needs to stop the van suddenly. Discuss how the unnecessary equipment, the rain and lack of sleep make this difficult.

4 State and explain which of the following pairs of vehicles will have the shortest stopping distances. Assume that everything other than the specified property is the same in both vehicles. a) A car with five heavy people in, and one with just a slim driver.

b) A tractor on a wet, muddy road, and one on a good dry road.

c) A car driven by a calm, well-rested person, and one driven by a harassed, tired person with screaming children in the back.

Crash Test Dummies!

Aim: To simulate an accident with crash test dummies to see the effect of inertia on them

Materials: Collision trolley, ruler, chalk, solid barrier (brick), plasticine, talcum powder, sticky tape

Method: 1. Mould a small plasticine person. Lightly powder it so that it is not sticky.2. Sit the plasticine person on the dynamics trolley.

Part A3. Set the ramp up on a shallow slope and let the trolley run down it and onto the

floor. Carefully note what happens to the plasticine person.4. Place a brick on the flat near the ramp’s end5. Model a head on collision by releasing the trolley from the first 20cm mark on the

ramp Repeat from the rest of the marks further up the ramp. Note what happens to the plasticine person, particularly to any parts of the body that moved a lot and any parts that moved a little. Test which mark up the ramp you consider to be ‘life threatening’ to the plasticine person.

Part B6. Build a sticky tape seat belt for the plasticine person and repeat. Are there any

differences in the results? What now is the ‘life threatening’ mark on the ramp?7. Take the belt off, but this time add a crumple zone to the front of the trolley.

Once again, what mark on the ramp is considered ‘life threatening’ this time?

Questions:1. Your backside is probably the least affected part of your body in a car crash.

Explain why inertia keeps heads, arms and legs moving but seems not to be as effective on your backside?

2. What stops the forwards movement in a car when no seatbelts are worn?3. What injuries would be likely in a head on collision while not wearing a seatbelt?4. Modern cars are designed to crumple in an accident. Why?5. What is the purpose of headrests in a car?

Questions for Dangerous driving1 If a car with a crumple zone crashes into a wall the front of the car decelerates more quickly than the middle. The

seat belts worn by the driver and passengers stretch when the car decelerates.(a) Explain the meaning of the terms in italics

(b) Why is it safer to have seat belts that stretch?

3 A roller-coaster train at rest has a mass of 30 tonnes. If a force of 50 000N acts on it for 12s then(a) What is its momentum after that time?

(b) What is its velocity?

4 A sports car travelling (illegally) at 40 m/s is involved in a car crash which stops it in a time of 2 s. The car had a mass of 1.5 tonnes (1 500 kg).(a) What was the momentum of the car before the crash?

(b) What was the average force decelerating it?

(c) The safety design of the car increased the time taken for the passenger to come to rest by 2 s. If she has a mass of 60 kg, what was the average force on the driver during the crash?

5 A climber falls off a cliff but is fortunately belayed by a rope. After fall for 1.5 seconds at an acceleration of 10 m/s2

the rope then brings the climber to rest in 0.5 seconds. The climber has a mass of 80 kg.(a) How fast is the climber going after 1.5 s?

(b) What is the momentum?

(c) What was the average resultant force which brought the climber to rest?

(d) What was the average tension in the rope as the climber came to rest?

timeA

B

CD

E

F

A graph of how a parachutist's downward velocity during his descent

X

Y

dow

nward

velocity

Terminal Velocity

a) Describe what is happening at points A to F.

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

b) What do the lines at X and Y signify?

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

c) How would the graph continue when the parachutist reaches the ground?

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

Year 10 Motion- Formula Sheet______________________________________________________Average distanceSpeed = time

______________________________________________________

Δ in speed a= m/s2 Δ in speed= m/s Acceleration = time taken t= seconds

______________________________________________________

Force = mass X acceleration a= m/s2 m= kgF= N

______________________________________________________

Weight = mass X gravity W= N m= Kg g= 9.8m/s2

Kinetic Energy = ½ X mass X speed X speed(joules) (kg) (m/s) (m/s)

Work = Force X Distance(joules) (Newtons) (m)

GravitationalPotential Energy = mass X acceleration due to gravity x height (joules) (kg) (9.8m/s2) (m)

Answers1 Speed and velocity1 a) 6 m/s

b) 120 mc) 5 s

2 c) i) 8 m/sii) zero

3 b) 280 m5 a) 10.2 m/s

2: Acceleration1 a) 6 m/s2

b) 80 m/sc) 25 s

2 a) 2 m/ s2

b) 1 m/ s2

3 A: 0.8 m/s2

B: 1.6 m/s2

C: 2.4 m/s2 (deceleration)4 50 m/s2

5 4 s

3: Force and acceleration1 b) 50 m/s2

2 a) 50 000 Nb) 20 000 Nc) 20 m/s2

3 14 000 N4 a) 1 500 N

b) 750 N5 a) 60 m/s

b) 40 m/s

4: Mass and acceleration2 a) 4.0 m/s2

b) 4.8 m/s2

3 100 m/s2

4 200 000 N5 a) 5 kg

b) 4 kg

5: Falling through the air2 a) 1 000 N

b) upward force < 1 000 Nc) 1 000 Nd) upward force > 1 000 N

3 a) 24 000 Nb) 40 m/s2

4 a) 700 Nb) 50 N upwardsc) 0.71 m/s2

5 a) 80 000 Nb) 120 000 Nc) 200 000 N

6: How much motion?1 a) 600 kg m/s

b) 36 000 000 kg m/sc) 0.240 kg m/s

2 a) 20 m/sb) 400 000 m/s

3 a) 40 m/sb) 1 m/s

4 a) 320 000 kg m/sb) 320 000 kg m/s

5 a) 200 kgb) 600 kg m/sc) 300 kgd) 2 m/s

7: Thinking, braking, stopping2 32 m3 unnecessary equipment →greater mass, longer braking distance rain→slippery roads, less friction, longer braking

distance lack of sleep→longer reaction time, longer thinking distance4 a) Good tyres, braking distance decreases

b) Slim driver, braking distance decreasesc) Dry road, braking distance decreasesd) Calm person, thinking distance decreases

5 400m vs. 100m, braking distance goes as square of speed, for 60 m/s this gives 900m

8: Dangerous driving3 a) 600 000 kg m/s

b) 20 m/s4 a) 60 000 kg m/s

b) 30 000 Nc) 600 N

5 a) 15 m/sb) 1 200 kg m/sc) 2 400 Nd) 3 200 N

Terminal Velocitya)

A The parachutist jumps out of the aeroplane. The only force acting at this instant is weight. The parachutist will have an acceleration of 10 m/s2. The graph has a steep gradient.

B Air resistance is increasing and the downward force is the same. Acceleration is decreasing so the gradient is less.C Air resistance equals weight, acceleration ceases, parachutist reaches terminal velocity.D The parachutist opens the parachute, air resistance is much greater than weight, so the parachutist decelerates

sharply, giving a steep gradient.E The parachutist is slowing down so air resistance is less although the weight is the same. Thus deceleration is less,

giving a less steep gradient.F Air resistance again equals weight so deceleration ceases, and the parachutist reaches a new, slower, terminal

velocity.

b)X represents terminal velocity without a parachute.Y represents terminal velocity with a parachute (much slower).c)When the parachutist reaches the ground the velocity drops sharply to zero.