Deck 9: Impulse and Momentum

Question 1

Two ice skaters push off against one another starting from a stationary position. The 45.0-kg skater acquires a speed of 0.375 m/s. What speed does the 60.0-kg skater acquire? Assume that any other unbalanced forces during the collision are negligible.

A) 0.500 m/s
B) 0.281 m/s
C) 0.375 m/s
D) 0.750 m/s
E) 0.000 m/s

Answer 1

0.281 m/s

Question 2

As a tile falls from the roof of a building to the ground its momentum is conserved.

Answer 2

False

Question 3

Two automobiles traveling at right angles to each other collide and stick together. Car A has a mass of 1200 kg and had a speed of 25 m/s before the collision. Car B has a mass of 1600 kg. The skid marks show that, immediately after the collision, the wreckage was moving in a direction making an angle of 40° with the original direction of car A. What was the speed of car B before the collision, assuming that any other unbalanced forces are negligible?

A) 16 m/s
B) 18 m/s
C) 11 m/s
D) 21 m/s
E) 14 m/s

Answer 3

16 m/s

Question 4

A time-varying horizontal force F(t) = At⁴ + Bt² acts for 0.500 s on a 12.25-kg object, starting at time t = 1.00 s. In the SI system, A has the numerical value 4.50 and B has the numerical value 8.75.
(a) What are the SI units of A and B?
(b) What impulse does this force impart to the object?

Question 5

You are standing on a skateboard, initially at rest. A friend throws a very heavy ball towards you. You can either catch the object or deflect the object back towards your friend (such that it moves away from you with the same speed as it was originally thrown). What should you do in order to MINIMIZE your speed on the skateboard?

A) Catch the ball.
B) Deflect the ball.
C) Your final speed on the skateboard will be the same regardless whether you catch the ball or deflect the ball.

Question 6

Consider two less-than-desirable options. In the first you are driving 30 mph and crash head-on into an identical car also going 30 mph. In the second option you are driving 30 mph and crash head-on into a stationary brick wall. In neither case does your car bounce off the thing it hits, and the collision time is the same in both cases. Which of these two situations would result in the greatest impact force?

A) hitting the other car
B) hitting the brick wall
C) The force would be the same in both cases.
D) We cannot answer this question without more information.
E) None of these is true.

Question 7

A car heading north collides at an intersection with a truck of the same mass as the car heading east. If they lock together and travel at 28 m/s at 46° north of east just after the collision, how fast was the car initially traveling? Assume that any other unbalanced forces are negligible.

A) 40 m/s
B) 20 m/s
C) 80 m/s
D) 30 m/s

Question 8

During a collision with a wall, the velocity of a 0.200-kg ball changes from 20.0 m/s toward the wall to 12.0 m/s away from the wall. If the time the ball was in contact with the wall was 60.0 ms, what was the magnitude of the average force applied to the ball?

A) 40.0 N
B) 107 N
C) 16.7 N
D) 26.7 N
E) 13.3 N

Question 9

A stationary 1.67-kg object is struck by a stick. The object experiences a horizontal force given by
F = at - bt², where t is the time in milliseconds from the instant the stick first contacts the object.
If a = 1500 N/(ms) and b = 20 N/(ms)², what is the speed of the object just after it comes away from the stick at t = 2.74 ms?

A) 3.3 m/s
B) 22 m/s
C) 3.7 m/s
D) 25 m/s

Question 10

A plate falls vertically to the floor and breaks up into three pieces, which slide along the floor. Immediately after the impact, a 320-g piece moves along the x-axis with a speed of 2.00 m/s and a 355-g piece moves along the y-axis with a speed of 1.50 m/s. The third piece has a mass of 100 g. In what direction does the third piece move? You can neglect any horizontal forces during the crash.

A) 216.9° from the x-axis
B) 219.8° from the x-axis
C) 36.9° from the x-axis
D) 39.9° from the x-axis
E) 39.8° from the x-axis

Question 11

A 2.50-kg stone is dropped from rest at a height of 3.75 m. What impulse does gravity impart to this stone from the instant it is dropped until it hits the ground, assuming negligible air resistance?

Question 12

A 480-kg car moving at 14.4 m/s hits from behind a 570-kg car moving at 13.3 m/s in the same direction. If the new speed of the heavier car is 14.0 m/s, what is the speed of the lighter car after the collision, assuming that any unbalanced forces on the system are negligibly small?

A) 13.6 m/s
B) 10.5 m/s
C) 19.9 m/s
D) 5.24 m/s

Question 13

A small glider is coasting horizontally when suddenly a very heavy piece of cargo falls out of the bottom of the plane. You can neglect air resistance. Just after the cargo has fallen out

A) the plane speeds up and the cargo slows down.
B) the plane speeds up but the cargo does not change speed.
C) neither the cargo nor the plane change speed.
D) the cargo slows down but the plane does not change speed.
E) both the cargo and the plane speed up.

Question 14

A 1.2-kg spring-activated toy bomb slides on a smooth surface along the x-axis with a speed of 0.50 m/s. At the origin 0, the bomb explodes into two fragments. Fragment 1 has a mass of 0.40 kg and a speed of 0.90 m/s along the negative y-axis. In the figure, the angle θ, made by the velocity vector of fragment 2 and the x-axis, is closest to

A) 31°.
B) 37°.
C) 38°.
D) 53°.
E) 59°.

Question 15

A firecracker breaks up into several pieces, one of which has a mass of 200 g and flies off along the x-axis with a speed of 82.0 m/s. A second piece has a mass of 300 g and flies off along the y-axis with a speed of 45.0 m/s. What are the magnitude and direction of the total momentum of these two pieces?

A) 361 kg∙m/s at 56.3° from the x-axis
B) 93.5 kg∙m/s at 28.8° from the x-axis
C) 21.2 kg∙m/s at 39.5° from the x-axis
D) 361 kg∙m/s at 0.983° from the x-axis
E) 21.2 kg∙m/s at 56.3° from the x-axis

Question 16

A 1000-kg car approaches an intersection traveling north at 20.0 m/s. A 1200-kg car approaches the same intersection traveling east at 22.0 m/s. The two cars collide at the intersection and lock together. Ignoring any external forces that act on the cars during the collision, what is the velocity of the cars immediately after the collision?

A) 29.7 m/s in a direction 47.7° east of north
B) 21.1 m/s in a direction 47.7° west of south
C) 15.1 m/s in a direction 52.8° east of north
D) 21.1 m/s in a direction 52.8° east of north
E) 21.1 m/s in a direction 47.7° east of north

Question 17

In a collision between two objects having unequal masses, how does magnitude of the impulse imparted to the lighter object by the heavier one compare with the magnitude of the impulse imparted to the heavier object by the lighter one?

A) The lighter object receives a larger impulse.
B) The heavier object receives a larger impulse.
C) Both objects receive the same impulse.
D) The answer depends on the ratio of the masses.
E) The answer depends on the ratio of the speeds.

Question 18

A 900-kg car traveling east at 15.0 m/s collides with a 750-kg car traveling north at 20.0 m/s. The cars stick together. Assume that any other unbalanced forces are negligible.
(a) What is the speed of the wreckage just after the collision?
(b) In what direction does the wreckage move just after the collision?

Question 19

A small car has a head-on collision with a large truck. Which of the following statements concerning the magnitude of the average force due to the collision is correct?

A) The truck experiences the greater average force.
B) The small car experiences the greater average force.
C) The small car and the truck experience the same average force.
D) It is impossible to tell since the masses are not given.
E) It is impossible to tell since the velocities are not given.

Question 20

Two objects of the same mass move along the same line in opposite directions. The first mass is moving with speed v. The objects collide, stick together, and move with speed 0.100v in the direction of the velocity of the first mass before the collision. What was the speed of the second mass before the collision?

A) 1.20v
B) 10.0v
C) 0.900v
D) 0.800v
E) 0.00v