Systems and Center of Mass

AP Physics 1· difficulty 3/5

A 60 kg60~\text{kg} person stands at one end of a 120 kg120~\text{kg}, 4.0 m4.0~\text{m} long boat at rest in still water. He walks to the other end. Ignoring water resistance, the boat shifts (relative to water) by

  • A

    1.0 m1.0~\text{m} opposite to walking direction

  • B

    2.0 m2.0~\text{m} opposite

  • C

    1.3 m1.3~\text{m} opposite to walking direction

    check_circle
  • D

    00

Explanation

Center of mass doesn't move. Person shifts +Δxp+\Delta x_p, boat shifts Δxb-\Delta x_b. With 60(Δxp)=120(Δxb)60(\Delta x_p) = 120(\Delta x_b) and Δxp+Δxb=4.0\Delta x_p + \Delta x_b = 4.0: Δxb=4.060/(60+120)1.33 m\Delta x_b = 4.0 \cdot 60/(60+120) \approx 1.33~\text{m}.

Want 10 more like this — adaptive to your weak spots?

Related questions