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Reference Frames and Relative Motion

AP Physics 1· difficulty 4/5

v_b v_c start

A boat travels at vb=4.0 m/sv_b = 4.0\text{ m/s} relative to water, aimed straight across a w=120 mw = 120\text{ m} river. The current flows at vc=3.0 m/sv_c = 3.0\text{ m/s}. How far downstream does the boat land?

  • A

    90 m

    check_circle
  • B

    60 m

  • C

    120 m

  • D

    75 m

Explanation

Crossing time: t=w/vb=120/4=30 st = w/v_b = 120/4 = 30\text{ s}. Downstream drift: Δx=vct=3×30=90 m\Delta x = v_c t = 3 \times 30 = 90\text{ m}.

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