AP Physics C Mechanics 4.2: Impulse and Momentum Change

Connect impulse to a system’s change in momentum and use the impulse–momentum theorem to relate force, time, and motion.

[Maximum number: 1]

Scientists have created a new type of lightweight foam and are performing experiments to investigate the properties of the foam. The mass of Cart A is 1000 kg and the mass of Cart B is 2000 kg. A piece of foam with negligible mass is attached to the front of Cart A, as shown. Cart A moves with a constant speed toward Cart B, which is initially at rest. At time $t=0 \mathrm{~s}$ , the foam connected to Cart A makes contact with Cart B. The foam remains in contact with Cart B for 0.5 s, after which the carts separate and both carts move with constant velocities.

Figure for Question 4.2.B—Describe the relationship between the impulse exerted on an object or system and the change in momentum of the… question 1 — AP Physics C: Mechanics

What is the relationship between the magnitude of the average net force $F_{1}$ exerted on Cart B for the collision with the foam and the magnitude of the average net force $F_{2}$ exerted on Cart B for the collision without the foam? $F_{1}>F_{2}$ $F_{1}<F_{2}$ $F_{1}=F_{2}$
Justify your answer.

For selecting $F_{1}<F_{2}$ with an attempt at a relevant justification

1 point

For indicating that the impulse or change in momentum of each cart in both collisions is the
same

1 point

For indicating that decreasing the time of collision means the average force must be greater

1 point

Example Solution
Since the initial and final velocities are the same for both collisions, $\Delta p$ is the same for both collisions; as a result, the impulse is the same for both collisions. So, if $\Delta t$ is smaller, $F_{\text {avg }}$ is larger.

Total for part (c)

for question 1

15 points

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4.2.B—Describe the relationship between the impulse exerted on an object or system and the change in momentum of the… question 1