Formative AssessmentsScience Grade 9 Physics Forces Unit

Statements in blue are the supporting learning targets for the question that follows.

ST3 I can explain that inertia is the property of an object that causes it to resist changes in motion.

Q. Explain why the student in the picture was able to remove the table cloth without having the dishes fall.

The inertia of the dishes kept them from moving when the table-cloth was quickly removed.

Q. A ball is rolled into a large metal rim and follows the dotted line as it goes around the rim. Which of the three paths will the ball take when it leaves the rim at the point shown?

The will follow path 2 since an object in motion will continue in motion in a straight line path unless acted upon by a force.

ST5 I can differentiate between constant and changing motion.

Q. Which of these graphs represent constant motion and which represent changing motion.

Constant motion are graphs a, b and d

Changing motion are graphs c, e and f

ST1 I can identify objects in equilibrium and not in equilibrium.

Q. For an object to be in equilibrium, what must be true?

The net force on the object must be zero

ST7 I can explain the acceleration of an object subjected to a set of forces in one dimension.

Q. A 10 kg mass on a horizontal friction–free table is accelerated by a string attached to another 10 kg mass hanging vertically from a pulley What is the acceleration of the system of both masses?

½ g

I can calculate the acceleration of an object subjected to a set of forces in one dimension: F= ma

Q. The 25 kg skater is propelled by rocket power with a thrusting force of 100 N and friction is 20 N. What is the skater’s acceleration?

100 N – 20N = 80 N a = F/m = 80 N/25 kg = 3.2 m/s

I can identify that whenever one object exerts force on another, a force equal in magnitude and opposite in direction is exerted by the second object back on the first object.

No it can’t be done. The scales will always read the same because of Newton’s 3rd Law. You pull on your friend and your friend pulls on you in the same interaction.

Q. You are sitting in a chair. The earth is pulling you down towards the earth. The reaction to this force is:

A. The chair pushing you upwards

B. You pulling up on the earth

C. You pushing the chair down

D. The air pushing you down

The answer is A.

I can use vectors and free-body diagrams to describe force and the position of objects in one-dimensional space.

Q. On each car draw the relative velocity vector for the car over time. What can you say about the force needed to account for any differences in the velocity vectors? There is friction between the cars and the road.

Car 1:

The velocity vectors should all be the same size and direction, since the car has a constant motion. Forces must be balanced, car is in equilibrium.

Car 2:

The velocity vectors should get larger as the car moves forward covering a greater distance each second. There is a net force acting on the car; the car is accelerating.

I can combine vectors in one-dimension to determine the resultant vector.

Q. You and your friend are asked by your teacher to pull on a pair of scales attached to the ends of a horizontal rope, so that the readings on the scales will be different. Can this be done? Explain.

Q. Dropping supplies, a plane flies 700 km west one day. The next day it flies 600 km east. Then it flies 300 km west and on the next day 400 km east. How far away is theplane from where it first began?

0 km away

*****2-D Don’t benchmark assess but can do formative, such as:

Q. Looking for a nesting site, a bird flies 7 km west one day. The next day it flies 6 km south. Then it flies 3 km east and on the next day 4 km north. How far away is the bird from where it first began?

4.47 km away

I can calculate and analyze the momentum of an object.

Q. What is the momentum of a 3000 kg elephant running at 5 m/s?

P = mv = 3000kg * 5 m/s = 15,000 kg m/s

Q. A small mouse and a large elephant are running at the same speed, which has a greater momentum?

The elephant, due to its small mass.

Q. Which has greater momentum? A car traveling 10 m/s or the same car traveling 30 m/s?

The car traveling 30 m/s, greater velocity means greater momentum.

I can calculate and analyze the changes in momentum as a result of forces on the object.

Q. Car companies test their vehicles for safety by crash testing them. If a 1500 kg car traveling at 15 m/s hits a cement wall and the impact brings the car to a stop in 0.08 s. What is the momentum of the car just before hitting the wall? With what average force is it brought to rest?

Momentum is mv = 1500 kg(15 m/s) = 22500 kg m/s

Ft = mv or F = mv/t = (22500 kg m/s)/(0.08 s) = 2.8 x105 N

Q. Using what you know about force, time, and change in momentum, explain why you’d rather land on sand and not concrete when jumping down from a large rock.

The sand has more “give”, meaning it will take longer for your body to stop, so less force. Landing on concrete, the concrete will stop you in a small amount of time, with a greater force on your body. Both situations have the same change in momentum. Concrete: Ft= m∆v sand: fT= m∆v

I can use gravitational force to explain the motion of objects near Earth.

Q. An apple drops from a tree, neglecting air resistance (so free fall), explain what happens to the motion of the apple and why.

The apple accelerates, traveling faster and farther each second, a net force acts on the apple.

Q. A feather is dropped out a window, assuming air resistance is present, explain what happens to the motion of the feather.

The feather accelerates due to gravity, but as its velocity increases the force of air resistance increases. Due to its small mass (and small force of gravity) the force of air resistance quickly equals the force of gravity – the feather reaches equilibrium and no accelerates, maintains a constant velocity, terminal velocity.

I can use the acceleration of gravity to determine the velocity and distance fallen for an object in free fall.

Q. A Student throws a ball into the air at 30 m/s. What is the velocity and distance from the student during each second of its flight? Add your answers to the figure.

at 1 s v = 20 m/s x = 25 m

at 2 s v = 10 m/s x = 40 m

at 3 s v = 0 m/s x = 45 m

at 4 s v = 10 m/s x = 40 m

at 5 s v = 20 m/s x = 25 m

at 6 s v = 30 m/s x = 0 m

at 7 s v = 40 m/s x = 35 m

Forces Unit Formative Assessments

LT/ST Question/Answer Source

Laws of Motion ST10, 7

A student is driving her car when an insect strikes her windshield.

1. Which of the following statements best describes the forces in this situation?

A. The insect strikes the windshield with the same force as the windshield strikes the insect.

B. The insect strikes the windshield with a force, and the windshield exerts no force on the insect.

C. The insect exerts no force on the windshield, and the windshield strikes the insect with a large force.

D. The insect strikes the windshield with a small force, and the windshield strikes the insect with a large force.A

2. Which object experiences the greater acceleration due to the collision?

A. The car

B. The insect

C. They experience the same acceleration

D. Neither object experiences an acceleration

B

MCAS 2011

#29

And MPS

Laws of Motion

ST5

The graph below shows the distance an object traveled over time.

3. Which line segment represents the time interval during which the object was moving

MCAS 2011

#31

and MPS

at a positive constant speed?

A. segment WB. segment XC. segment YD. segment Z

C.

4. Which line segment represents the time interval during which the object was increasing its speed?

A. segment WB. segment XC. segment YD. segment Z

A.

5. In line segment X, the object is

A. moving the fastestB. not movingC. moving 20 m/sD. moving, but slowly

B.

Laws of Motion

ST11

6. A meteoroid with a mass of 1,000 kg enters Earth’s atmosphere with a velocity of 4,400 m/s. What is the magnitude of the meteoroid’s momentum at that instant?

A. 44 kg • m/sB. 2,200,000 kg • m/sC. 4,400,000 kg • m/sD. 9,680,000,000 kg • m/s

C.

MCAS 2011

#41

Vectors ST2

7. Four students push on a block of wood with the forces shown in the diagram below. Assume friction is negligible.

The block slides horizontally. What is the net force acting on the block of wood?

A. 3 N to the leftB. 8 N to the leftC. 11 N to the rightD. 25 N to the right

MCAS 2010

#2

C

Laws of Motion ST11

8. The momentum of an object in space is

A. dependent on its mass.B. independent of its inertia. C. independent of its velocity.D. dependent on its potential energy.

A

MCAS 2010

#8

Laws of Motion

ST5, 2, 7,8

9. A student is conducting experiments with a block of wood. In experiment 1, the student pulls the block of wood with a constant force of 10 N along a horizontal surface. In experiment 2, the student pulls the same block of wood with a constant force of 10 N. The type of surface is different from that used in experiment 1. The results of experiments 1 and 2 are shown below.

A. Using information from the graphs, compare the friction of the surface in experiment 2 with the friction of the surface in experiment 1.In experiment 2, the block of wood had a constant velocity, no acceleration, so the surface had a greater friction (than in expt 1), equal to the 10 N pulling force. In expt 1, the block shows an acceleration, so the force of friction is less than the force of the pull, there is a net force.

B. Determine both the magnitude of the force of friction and the net force on the block that are required to achieve the results shown in the graph for experiment 2. Include units in your answer.F fric = -10N, Fnet = 0N, (a = 0 m/s2)

C. Without changing the type of surface used when pulling the block of wood, list one other change to experiment 1 that would produce the results of experiment 2. Explain your reasoning with reference to the frictional force.Pull the object with less force to match the force of friction, (as set, the pull is greater than the force of friction, so it has a net force, is accelerating), this will reduce the net force to zero.

MCAS 2010

#23

Vectors ST14

A 2000 kg car is pulling a 1000 kg trailer. The car’s engine exerts a 6000 N force to move the car and the trailer. In addition, the car and the trailer each experience a 1000 N frictional force as they are being pulled, as represented below.

MCAS 2010

Laws of Motion

ST7

10. What is the magnitude of the net force on this system?

A. 2000 NB. 4000 NC. 5000 ND. 8000 N

B

11. What is the acceleration of the system?

A. 2 m/s2

B. 3 m/s2

C. 1.33 m/s2

D. 2.6 m/s2

C

#26

Laws of Motion

ST10

Two students are standing next to each other on a level field. One of the students throws a table tennis ball forward toward a line 2.0 m away. At the same time, the second student throws a bowling ball in the same direction. Both balls take the same time to travel the 2.0 m.

Only the second student feels a noticeable backward push when she throws her ball.

12. Which of the following statements explains why only the second student feels a noticeable backward push?

A. The bowling ball exerts a much larger reaction force.B. The bowling ball undergoes a much larger acceleration.C. The bowling ball requires more force to overcome gravity.D. The bowling ball converts more inertia into kinetic energy.

A

MCAS 2010

#34

Laws of Motion ST5

13. Which of the following will always change when an object accelerates?

A. massB. potential energyC. velocityD. weight

MCAS 2010

#37

C

Laws of Motion

ST5

The graph below shows the speed of an object during a 10 s time interval.

14. In which of the following time intervals is the speed of the object decreasing?

A. between 0 s and 2 sB. between 2 s and 4 sC. between 6 s and 8 sD. between 8 s and 10 s

D

15. In which of the intervals is the object moving the fastest?

A. between 0 s and 2 sB. between 2 s and 4 sC. between 6 s and 8 sD. between 8 s and 10 s

B

16. In which of the intervals is the object moving at a constant speed?

A. between 0 s and 2 sB. between 2 s and 4 sC. between 5 s and 6 sD. between 8 s and 10 s

B

MCAS 2010

#42

and MPS

Vectors ST2

The diagram below shows the forces acting on a rock.

17. The weight of the rock is 76 N. An upward force of 106 N is exerted on the rock. What is the net force acting on the rock?

A. 30 N upwardB. 76 N downwardC. 106 N upwardD. 182 N downward

A.

MCAS 2009

#2

Laws of Motion

ST5

A car has an oil drip. As the car moves, it drips oil at a regular rate, leaving a trail of spots on the road.

18. Which of the following diagrams of the car’s trail of spots shows the car continuously slowing down?

A

MCAS 2009

#14

Laws of Motion ST10

19. A toy cart that has a weight of 10 N moves with a constant velocity of 2 m/s to the right on a horizontal table. According to Newton’s laws of motion, which of the following statements is correct?

A. The table exerts a force of 10 N upward on the toy cart.B. The toy cart exerts a force of 10 N upward on the table.C. The toy cart exerts a force of 2 N downward on the table.D. The table exerts a force of 2 N to the right on the toy cart.

A

MCAS

2009

#19

Laws of Motion

ST7

20. A ball has a mass of 0.1 kg and an initial velocity of 20 m/s. The ball is given force of 3 N for 5 s.

What is the acceleration of the ball during the 5 seconds?

A. 0 m/s2

B. 30 m/s2

C. 0.033m/s2

MCAS 2009

#36

D. D. 0.3 m/s2

B

Laws of Motion ST11

21. Which of the following has the greatest momentum?

A. a 60 kg deer moving west at a speed of 20 m/sB. a 6300 kg elephant moving east at a speed of 0.10 m/sC. a 0.40 kg soccer ball moving downfield at a speed of 10 m/sD. a 0.03 kg arrow moving toward a target at a speed of 100 m/s

A

MCAS 2009

#37

Laws of Motion ST11

Mike, who has a mass of 75 kg, is running north at 2.6 m/s. He accidentally collides with Tom, who has a mass of 125 kg and is not moving.

22. Which of the following statements describes how much momentum each person has before the collision?

A. Mike has a momentum of 130 kg • m/s north, and Tom has no momentum.B. Mike has a momentum of 195 kg • m/s north, and Tom has no momentum.C. Both Mike and Tom have a momentum of 130 kg • m/s north.D. Both Mike and Tom have a momentum of 195 kg • m/s north.

B

MCAS 2008

#8

Laws of Motion ST2

23. A cart with a mass of 5 kg rests on a floor next to a wall, as shown in the diagram below.

A person pushes on the cart to the left toward the wall with a force of 100 N. Which of the following statements is true in this situation?

A. The wall does not push on the cart.B. The floor pushes 100 N up on the cart.C. The cart pushes 100 N down on the floor.

MCAS 2008

#16

D. The wall pushes 100 N to the right on the cart.D

Laws of Motion

ST2,7

24. A 1500 kg car has an applied forward force of 5000 N and experiences an air resistance of 1250 N.

24. What is the car’s acceleration?

A. 2.5 m/s2

B. 3.3 m/s2

C. 4.2 m/s2

D. 9.8 m/s2

A

MCAS 2009

#20

Laws of Motion

ST3

An astronaut in space is holding two identical sealed boxes. One is empty and the other is full of sand. The astronaut cannot open the boxes and the force of gravity is neglible.

25. What can the astronaut do to determine which box is which?

Shake each box

26. Describe the expected results for each box.

The box with sand has more mass, more inertia and will require more force to move at the same acceleration. The empty box has less mass, less inertia, less force is needed to change its motion.

MPS

Laws of Motion

ST3

While stopped at a red light, your car is hit from behind. Neck injuries are common from this kind of accident.

27. Using the concept of inertia, explain what happens to cause injury to your neck.

Your body was at rest, when hit from behind, your body moves forward with the car, but your hear and neck (not touching the car seat) will try to stay at rest, appearing as though your head gets whipped back.

MPS

Laws of Motion

ST3

28. While riding the bus, you place a ball on the floor of the aisle. The bus comes to a sudden stop. Explain what happens to the motion of the ball.

The ball has inertia of motion and continues to move forward, so it rolls forward on the bus.

MPS

Laws of Motion

ST10

ST11

29. A 1000 kg car traveling 20 m/s hits a tree with a force of 10,000N and comes to a stop. What is the force the tree exerts on the car?

A. 0 NB. 20,000 NC. 50 ND. 10,000 N

D

30. What is the car’s change in momentum that occurs as a result of the collision?

A. kg m/sB. 20,000 kg m/sC. 50 kg m/sD. 10,000 kg m/s

B

MPS

Laws of Motion ST 10

31. If the earth pulls you down with a force of 600 N. With what force do you pull up on the earth?

A. 0 NB. 10 NC. 600 ND. 6000 N

C

MPS

Vectors

ST13 ST14

Laws of Motion ST7

ST7,8

An 80 kg skydiver experiences a force of gravity of 800 N and a force of air resistance of 400 N.

32. Draw vectors to illustrate the forces on the skydiver. (label your scale)

33. Determine and draw the resultant force of the skydiver.

400N down

MPS

34. Determine the acceleration of the skydiver.

a = 400N/80kg = 5 m/s2

35. When the force of air resistance reaches 800 N, explain what happens to the motion of the skydiver.

When force of air resistance equals 800N, the net force is zero. The skydiver will not accelerate, but will continue falling at a constant velocity, called terminal velocity.

Laws of Motion ST2,7

36. Two students are in-line skating. The diagram below shows student S pushing student T. Student S has a mass of 60 kg,and student T has a mass of 40 kg.

36. Student S is pushing student T in a straight line with a force equal to the friction on student T’s skates. Which of the following must happen if student S continues to push student T with the same force?

A. Student T will lose his balance.B. Student T will travel in a circle.C. Student T will move at a constant velocity.D. Student T will move at a constant acceleration.

C

MCAS 2011

#19

ST6 A person is driving his car to a store. The store is 800 m north of the person’s starting point. After traveling north 1200 m, the person realizes that he has passed the store. He turns the car around and drives back to the store. Altogether, the trip to the store takes 100 s.

39. Determine the distance traveled by the car on this trip to the store. Show your calculations and include units in your answer.

1200 m + 400 m = 1600m

40. Calculate the average speed of the car on this trip. Show your calculations and include units in your answer.

1600m/100s = 1.6 m/s

41. Determine the displacement of the car for this trip. Include units in your answer.

800m north

MCAS 2011

#44

42. Calculate the average velocity of the car upon arrival at the store. Show your calculations and include units in your answer.

800m/100s = 8 m/s

ST6 The table below shows the time it takes four cars to go from 0 to 60 km/h.

43. Based on the information given, which of the following quantities can be compared for the four cars?

A. average accelerationB. instantaneous speedC. stopping distanceD. stopping time

A.

MCAS 2010

#40

ST6 The graph below shows velocity measurements made as a car moved north for 25 s.

44. How far did the car move during the first 15 s of the trip?

A. 20 mB. 25 mC. 300 mD. 500 m

C

MCAS 2009 #27