AP Physics 1 4.3: Selecting the Momentum System

Choose the momentum system boundary and determine whether external forces transfer momentum into or out of that selected system.

[Maximum number: 3]

A student has a cart of mass $m_{\mathrm{c}}$ and a block of mass $\frac{1}{5} m_{\mathrm{c}}$ , as shown in Figure 1.

- At time t=0, the cart is moving to the right across a horizontal surface with constant

speed $v_{\mathrm{c}}$ , and the student releases the block from rest.

- At $t=t_{1}$ , the block collides with and sticks to the top of the cart. The block does not slide

on the cart.

- At $t=t_{2}$ , the block-cart system continues to move to the right with constant speed $v_{f}$ .

Figure 1

Consider the case where a new block is dropped and collides with the top of the cart. The

new block slides along the cart during the collision but does not slide off the cart. The time

interval from when the new block collides with the cart and moves together with the cart

is $\Delta t$ . During $\Delta t$ there is a frictional force between the new block and the cart.

Indicate whether the x-component of the momentum of the new block-cart system increases,

decreases, or remains constant during $\Delta t$ .

Increases

Decreases

Remains constant

Justify your response.

All question bank results loaded

4.3.B—Describe how the selection of a system determines whether the momentum of that system changes question 1