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AP Physics 1: Algebra-Based 4.3 B Describe How the Selection of a System Determines Whether the Momentum of That System Changes Questions

Choose a momentum-system boundary, distinguish internal from external forces, and use centre-of-mass motion to identify momentum transfer.

Syllabus
Effective Fall 2024
Course
AP Physics 1: Algebra-Based

Exam points

  • choose a system boundary and classify contact, friction, engine or wall forces as internal or external
  • explain constant total momentum or centre-of-mass velocity when net external force is zero
  • infer external momentum transfer from a change in total momentum or centre-of-mass graph slope
  • explain why internal mass changes or paired forces do not create net system impulse

AP Physics 1: Algebra-Based 4.3 B Describe How the Selection of a System Determines Whether the Momentum of That System Changes Questions question 1

[Maximum number: 3]

A student has a cart of mass mcm_{\mathrm{c}} and a block of mass 15mc\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 vcv_{\mathrm{c}}, and the student releases the block from rest.

- At t=t1t=t_{1}, the block collides with and sticks to the top of the cart. The block does not slide on the cart.

- At t=t2t=t_{2}, the block-cart system continues to move to the right with constant speed vfv_{f}.

Figure 1

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 Δt\Delta t. During Δt\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 Δt\Delta t.

Increases Decreases Remains constant Justify your response.

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