2015-2016 - session 1 - cons of momentum & other mechanics.pdf

Mr. Carlos Ortiz | AMANDA LOPEZ-CARDET | IB PHYSICS PREPARATION of 19

Copyright © Carlos Ortiz 2015

PRACTICE 1

A ball of weight W is travelling horizontally towards a vertical wall. It strikes the wall and rebounds

horizontally. The change in the magnitude of the momentum of the ball is ∆p. Which of the following is the

magnitude of the impulse that the ball imparts to the wall?

A. W + ∆p

B. W – ∆p

C. W

D. ∆p remember, the magnitude of the impulse = CHANGE IN MOMENTUM = Δp

PRACTICE 2

A force F is applied to a body moving along a straight line. A resistive force f acts on the body.

Both forces act along the same straight line as the motion of the body. The rate of change of momentum of

the body is equal to

A. F – f. this one is a nice one – the rate of change of momentum = Δp/Δt and that EQUALS Fnet

…in this case, Fnet = the “sum” of all forces = F – f

B. F.

C. F + f.

D. f.

IB PHYSICS PREPARATION

Course: PHYSICS PREPARATION Delivered: Thursday, Aug 27, 2015

Instructor: Mr. Carlos Ortiz TBCB: NA

Student: Amanda Lopez-Cardet ETTC: 120 min

Behind every successful man is a

woman. Behind the downfall of that

man is usually another woman.

You do not need a parachute to

skydive. You need a parachute to

skydive TWICE!



PRACTICE 3

A stone attached to a string is moving in a horizontal circle. The constant speed of the stone is v.

The diagram below shows the stone in two different positions, X and Y.

Which of the following shows the direction of the change of velocity of the stone when moving from position

X to position Y?

if you think about it, the v vector must go from pointing DOWN ONLY to RIGHT

ONLY…so the CHANGE IN VELOCITY VECTOR must “eliminate the downward motion” and

“introduce a rightward motion”…SO IT MUST POINT UP AND TO THE RIGHT!

PRACTICE 4

Two objects undergo an inelastic collision. Which of the following is correct in respect of both the

conservation of momentum and the conservation of total energy of the system?

Momentum Total energy

A. conserved not conserved

B. conserved conserved

C. not conserved not conserved

D. not conserved conserved



PRACTICE 5

A constant force of magnitude F is applied to a mass m for a time interval ∆t. The magnitude of the impulse

given to the mass equals

A. m

F.

B. t

F

.

C. F∆t.

D. m

tF.

PRACTICE 6

Two carts of different mass m and M are connected by a spring. They are pushed together such that the spring

is compressed.

After the carts are released, the cart of mass m moves with velocity v. The change in the momentum of mass M

is

A. mv.

B. –mv.

since initially the total momentum = 0, then the total momentum AFTER must EQUAL “0” again…so

the only way that’ll happen is if the LEFT CART’S MOMENTUM is exactly OPPOSITE to the

momentum of the RIGHT CART…so –mv.

C. Mv.

D. –Mv.



PRACTICE 7

A rubber ball, travelling in a horizontal direction, strikes a vertical wall. It rebounds at right angles to the wall.

The graph below illustrates the variation of the ball’s momentum p with time t when the ball is in contact with

the wall.

Which of the following statements is true?

A. The shaded area is equal to the force exerted by the wall on the ball.

B. The shaded area is equal to the force exerted by the ball on the wall.

C. The gradient is equal to the force exerted by the wall on the ball.

Remember, gradient is another word for slope…so the slope any momentum vs. time graph will

always be FORCE

D. The gradient is equal to the force exerted by the ball on the wall.

PRACTICE 8

Two spheres of masses m1 and m2 are moving towards each other along the same straight-line with speeds v1

and v2 as shown.

The spheres collide. Which of the following gives the total change in linear momentum of the spheres as a

result of the collision?

A. 0

B. m1v1 + m2v2

C. m1v1 − m2v2

D. m2v2 − m1v1



PRACTICE 9

A tennis ball of mass m moving horizontally with speed u strikes a vertical tennis racket. The ball bounces

back with a horizontal speed v.

The magnitude of the change in momentum of the ball is

A. m(u + v).

B. m(u – v).

C. m(v – u).

D. zero.

PRACTICE 10

A brother and sister take the same time to run up a set of steps. The sister has a greater mass than her brother.

Which of the following is correct?

Has done the most work Has developed the greatest power

A. brother brother

B. brother sister

C. sister brother

D. sister sister

The sister has more MASS so she must exert a greater FORCE to lift her mass up the stairs…REMEMBER,

distanceWork performed ForceP

time time

The sister has a GREATER FORCE that she must exert…but her distance and time are the same as her brother’s…so her

greater FORCE means she is MORE POWERFUL because she did MORE WORK in the same time frame as her brother!



PRACTICE 11

A car of mass 1000 kg accelerates on a straight, flat, horizontal road with an acceleration

a = 0.3 m s–2

. The driving force F on the car is opposed by a resistive force of 500 N.

The net (resultant) force on the car is

A. 200 N.

B. 300 N.

C. 500 N.

D. 800 N.

PRACTICE 12

A nuclear power station produces 10 GW of electrical power. The power generated by the nuclear reactions in

the core of the reactor is 25 GW. The efficiency of the power station is

A. 15 %.

B. 35 %.

C. 40 %.

D. 60 %.

PRACTICE 13

A cyclist rides around a circular track at a uniform speed. Which of the following correctly gives the net

horizontal force on the cyclist at any given instant of time?

Net horizontal force along

direction of motion

Net horizontal force normal to

direction of motion

A. zero zero

B. zero (cyclist has uniform speed..no “a” = no “F”)

non zero (centripetal force acts here)

C. non zero zero

D. non zero non zero



PRACTICE 14

The graph shows the variation with time t of the acceleration a of an object.

Which of the following is the change in velocity of the object in the time interval 0 to 4 s?

A. –8 m s–1

B. –4 m s–1

C. +4 m s–1

D. +8 m s–1

PRACTICE 15

Which of the following is the condition for a body to be in translational equilibrium?

A. The resultant force on the body in any direction is zero.

B. The velocity of the body in any direction is zero.

C. No external force is acting on the body.

D. No work is done on the body.



PRACTICE 16

The graph shows the variation with force F of the extension s of a spring.

The work done in changing the extension of the spring from 3.0 cm to 6.0 cm is

A. 15 N cm.

B. 30 N cm.

C. 45 N cm. (this is just the AREA under the graph from s = 3cm to s = 6 cm)

D. 60 N cm.

PRACTICE 17

Which of the following is a correct definition of work?

A. Product of force and distance

B. Product of force and distance moved in the direction of the force

C. Product of power and time

D. Product of force and displacement



PRACTICE 18

Stephen pushes two boxes P and Q, that stay in contact, along a rough table, with a force F of 30 N.

Box P has a mass of 2.0 kg and box Q has a mass of 4.0 kg. Both boxes move with constant speed.

The resultant force on box Q is

A. 0 N. the key here is that the both boxes move with constant speed = that means the NET or

RESULTANT FORCE MUST EQUAL “0”

B. 5.0 N.

C. 15 N.

D. 30 N.

PRACTICE 19

A ball moves along the inside of a horizontal semi-circular ring as shown. The diagram is a view from above.

Which arrow represents the direction of the average force on the ball?

here, I’ve drawn 5 arrows that would represent the FORCE on the ball at 5 points along its path…notice they

are all POINTING TO THE CENTER (centripetal)…the bottom two arrows point UP and LEFT…the

top two arrows point DOWN and LEFT….the UP and DOWN parts CANCEL…leaving only the LEFT

PARTS…the middle arrow points ONLY LEFT…so in the end, the NET direction is LEFT!



PRACTICE 20

A ball is thrown vertically upwards and comes down again. Air resistance is negligible. Which of the following

graphs shows how the gravitational potential energy EP varies with time t?

Amanda, when ball is first thrown, its gravitational potential energy, or Ep is “0” because it is at its

lowest point..it the ball then CLIMBS to its highest point at which time it has its HIGHEST Ep …and

then it falls back down and its Ep goes back to “0”

PRACTICE 21

A pump extracts water from a well of depth h at a constant rate of R kg s–1

. What is the power required to raise

the water?

A. gh

R

B. Rgh

C. h

Rg

D. R

hg



PRACTICE 22

A cart of mass M is on a horizontal frictionless table.

The cart is connected to an object of weight W via a pulley. Which of the following is the acceleration of the

cart?

A. W

g

WM

B.

g

WM

W

C. W

Mg

D. 0



PRACTICE 23

A ball falls vertically and bounces off the ground. Immediately before impact with the ground the speed of the

ball is u. Immediately after leaving the ground the speed is v.

Which of the following expressions is the ratio of collision beforey immediatelenergy kinetic

collisionon lost energy kinetic?

A. u

v

B. u

v1

C.

2

u

v

D.

2

1

u

v



PRACTICE 24

A raindrop falling from rest at time t = 0 reaches terminal velocity. Which graph best represents how the speed

v varies with time t?

PRACTICE 25

A railway engine of mass m moves along a horizontal track with uniform speed v. The total resistive force

acting on the engine is F.

Which of the following is the power of the engine?

A. mv

F

B. Fv

C. F

mv

D. F

v



PRACTICE 26

A gas atom strikes a wall with speed v at an angle θ to the normal to the wall. The atom rebounds at the same

speed v and angle θ.

Which of the following gives the magnitude of the momentum change of the gas atom?

A. zero

B. 2mv sinθ

C. 2mv

D. 2mv cosθ

PRACTICE 27

A net force of magnitude 4.0 N acts on a body of mass 3.0 kg for 6.0 s. The body is initially at rest. Which of

the following is the speed of the body after the 6.0 s interval?

A. 0.50 m s–1

B. 2.0 m s–1

C. 4.5 m s–1

D. 8.0 m s–1



PRACTICE 28

A car moves from X to Y along a semicircular path. The radius of the path is 250 m and the time taken to

complete the trip is 50 s.

Which of the following correctly shows the magnitude of the average velocity and the magnitude of the

average speed?

Average velocity Average speed

A. 10 m s–1

10 m s–1

B. 10 m s–1

16 m s–1

C. 16 m s–1

10 m s–1

D. 16 m s–1

16 m s–1

Amanda, remember that displacement distance

time timeavg velocity while avg speed

in this case, the DISPLACEMENT from X to Y is straight to the right = THE DIAMETER of the

semicircle = 500m….so avg. velocity = 500 m/50 s = 10 m s-1…

now, the DISTANCE is MORE…it is the distance ALONG THE SEMICIRCLE…so u have to

calculate a HALF-CIRCUMFERENCE or r = (250m) = 785.4 m…

so the avg. speed = 785.4 m/50 s ≈ 16 m s-1…

PRACTICE 29

A skydiver jumped out of an airplane. On reaching a terminal speed of 60 m s–1

, she opened her parachute.

Which of the following describes her motion after opening her parachute?

A. She went upwards for a short time, before falling to Earth at a speed of 60 m s–1

.

B. She continued downwards at 60 m s–1

, but hit the ground with less force.

C. She continued to fall but reached a new terminal speed of less than 60 m s–1

.

D. She went upwards for a short time, before falling to Earth at a speed of less than 60 m s–1

.



PRACTICE 30

The diagram shows a girl attempting (but failing) to lift a heavy suitcase of weight W. The magnitude of the

vertical upwards pull of the girl on the suitcase is P and the magnitude of the vertical reaction of the floor on

the suitcase is R.

Which equation correctly relates W, P and R?

A. W = P + R

B. W > P + R

C. W < P + R

D. W = P = R



PRACTICE 31

A ball, initially at rest, is dropped in the air from a great height. Air resistance is not negligible.

Which of the following graphs best shows the variation with time t of the acceleration a of the ball?

PRACTICE 32

A constant force of magnitude F is applied to a mass m for a time interval ∆t. The magnitude of the impulse given to

the mass equals

A. m

F.

B. t

F

.

C. F∆t.

D. m

tF.



PRACTICE 33

A lamp of weight W is suspended by a wire fixed to the ceiling. With reference to Newton’s third law of

motion, the force that is equal and opposite to W is the

A. tension in the wire.

B. force applied by the ceiling.

C. force exerted by the lamp on the Earth.

Amanda, remember, the EARTH pulls on the lamp…and this “pull” is the lamp’s weight W; the

LAMP reciprocates and pulls back

D. force exerted by the Earth on the lamp.

PRACTICE 34

The Moon orbits the Earth.

Which of the following diagrams correctly represents the force(s) acting on the Moon?

PRACTICE 35

Two balls of different mass are dropped from the top of a tall building one after the other. The distance

between the balls

A. increases with time.

B. depends on the initial velocity only.

C. remains constant.

D. depends on the mass of the balls.



PRACTICE 36

The graph shows how the velocity of a particle varies with time.

Which of the following graphs correctly shows how the acceleration of the particle varies with time?

2015-2016 - session 1 - cons of momentum & other mechanics.pdf

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