AP Physics 1 · Topic 4.2

Change in Momentum and Impulse Practice

Part of Linear Momentum.(TOP-4.B)

Practice questions

23

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Sample questions

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  1. Sample 1difficulty 1/5

    A constant force of 20 N20~\text{N} acts on an object for 0.25 s0.25~\text{s}. What impulse does it deliver?

    • A

      5.0 N⋅s5.0~\text{N·s}

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    • B

      500 N⋅s500~\text{N·s}

    • C

      0.80 N⋅s0.80~\text{N·s}

    • D

      80 N⋅s80~\text{N·s}

    Why

    J=FΔt=(20)(0.25)=5.0 N⋅sJ = F \Delta t = (20)(0.25) = 5.0~\text{N·s}.

  2. Sample 2difficulty 1/5

    A 0.20 kg0.20~\text{kg} ball at 5 m/s5~\text{m/s} is struck and rebounds at 5 m/s5~\text{m/s} (opposite direction). The impulse is

    • A

      00

    • B

      10 N⋅s10~\text{N·s}

    • C

      1 N⋅s1~\text{N·s}

    • D

      2 N⋅s2~\text{N·s}

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    Why

    J=Δp=m(vfvi)=0.20(5(5))=2 N⋅sJ = \Delta p = m(v_f - v_i) = 0.20(5 - (-5)) = 2~\text{N·s}.

  3. Sample 3difficulty 2/5

    For the same ball above, if it instead <strong>rebounds</strong> elastically at 6 m/s6~\text{m/s}, the impulse from the wall is

    • A

      00

    • B

      12 N⋅s12~\text{N·s}

    • C

      6 N⋅s6~\text{N·s}

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    • D

      3 N⋅s3~\text{N·s}

    Why

    Δp=(0.5)(6)(0.5)(6)=6 kg⋅m/s\Delta p = (0.5)(-6) - (0.5)(6) = -6~\text{kg·m/s} (impulse magnitude 6 N⋅s6~\text{N·s} — twice the absorption case).

  4. Sample 4difficulty 2/5

    A 0.5 kg0.5~\text{kg} ball at 6 m/s6~\text{m/s} hits a wall and sticks. The impulse from the wall on the ball is

    • A

      1.5 N⋅s1.5~\text{N·s}

    • B

      6 N⋅s6~\text{N·s}

    • C

      00

    • D

      3 N⋅s3~\text{N·s}

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    Why

    Δp=0(0.5)(6)=3 kg⋅m/s\Delta p = 0 - (0.5)(6) = -3~\text{kg·m/s}. Magnitude 3 N⋅s3~\text{N·s}.

  5. Sample 5difficulty 2/5

    0 2 4 4 12 t (s) p (kg·m/s)

    The graph shows an object's momentum over time. What impulse was delivered to the object at t=2 st = 2~\text{s}?

    • A

      4 N⋅s4~\text{N·s}

    • B

      12 N⋅s12~\text{N·s}

    • C

      16 N⋅s16~\text{N·s}

    • D

      8 N⋅s8~\text{N·s}

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    Why

    Impulse equals the change in momentum: Δp=124=8 N⋅s\Delta p = 12 - 4 = 8~\text{N·s}.