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PRACTICE / Relative motion

Rain seen from a moving trolley

Rain falls vertically at 12 m/s relative to the ground. A trolley moves horizontally at 5 m/s.

Find the speed of rain relative to the trolley.

Organize the givens & assumptions
  • rain = (0, −12) m/s
  • trolley = (5, 0) m/s

Uniform rain and trolley velocities on perpendicular ground-frame axes; use nonrelativistic velocity subtraction.

  1. A12 m s−112\ \mathrm{m\,s^{-1}}
  2. B13 m s−113\ \mathrm{m\,s^{-1}}
  3. C17 m s−117\ \mathrm{m\,s^{-1}}
  4. D7 m s−17\ \mathrm{m\,s^{-1}}

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