AP®PhysicsCollege BoardPhysics 1: Algebra-BasedExam QuestionsUnit 2: Force & Translational DynamicsSystems & Center of Mass

Systems & Center of Mass (College Board AP® Physics 1: Algebra-Based)

Exam Questions

5 mins5 questions
1
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Diagram showing a ramp with an object labelled M at the top, sliding down towards a block labelled 2M on a flat surface. Distance D is marked.

A small block of mass M is released from the top of a curved frictionless ramp, as shown in the figure. The block slides down the ramp until it collides with a larger block of mass 2 M which is at rest at the bottom of the ramp. After the collision, the larger block moves along a rough horizontal surface before coming to rest after a distance D.

By considering the mechanical energy of the two-block-Earth system, which of the following statements is correct, and why?

  • The system is open, because there is a net force exerted on the larger block.

  • The system is open, because the small block’s initial velocity and the larger block's final velocity is zero.

  • The system is closed, because there is a net force exerted on the larger block.

  • The system is closed, because the small block’s initial velocity and the larger block's final velocity is zero.

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21 mark
Three spheres on a horizontal line at coordinates 1m, 2m, and 4m, weighing 1kg, 2kg, and 8kg, respectively; x-axis labelled from 0 to 5m.

Three objects are arranged along the x-axis, as shown in the figure.

Which of the following is most nearly the location of the center of mass of the objects?

  • 3.0 space straight m from the origin

  • 2.4 space straight m from the 1 kg object

  • 0.6 space straight m from the 2 kg object

  • 0.4 space straight m from the 8 kg object

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3
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Grid with four horizontal and vertical lines. Points labelled 1-4, with weights annotated: 3 kg at top, 1 kg and 3 kg right, 7 kg bottom left.

Four objects are arranged in a plane, as shown in the figure.

Which of the following points represents the location of the center of mass of the objects?

  • 1

  • 2

  • 3

  • 4

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4
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Diagram of a ruler with numbers 1-17 balanced on a triangular pivot. A ring on 2, and two rings on 14. A labelled peg at the right end.

A uniform rod is balanced on a pivot, as shown in the figure. Rings of equal mass are hung on different pegs, two on peg 14, and one on peg 2.

If a fourth ring is hung on peg 6 to balance the rod, which of the following correctly describes how the center of mass of the system changes?

  • The center of mass shifts to the left by 1 peg

  • The center of mass shifts to the right by 1 peg

  • The center of mass shifts to the left by 2 pegs

  • The center of mass shifts to the right by 2 pegs

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5
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Diagram of a pulley system with a single rope. Block X hangs lower than block Y, both suspended by the pulley from the ceiling.

Objects X and Y are connected by a string of negligible mass and suspended vertically over a pulley of negligible mass, as shown in the figure. The objects are initially held at rest, and the mass of Object Y is greater than the mass of Object X. All frictional forces are considered to be negligible.

How do the mechanical energies of the two-object–string system and the two-object–string-Earth system change from when the objects are released to when they return to rest?

Two-Object-String System

Two-Object-String-Earth System

A

Decreases

Increases

B

Increases

Decreases

C

Decreases

Remains Constant

D

Remains Constant

Remains Constant

  • (A)

  • (B)

  • (C)

  • (D)

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