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PRACTICE · MEMBERSIntermediate · Single correct

PRACTICE / River crossing

Crossing without being swept downstream

A swimmer can move at 5 m/s through water. A river flows at 3 m/s and is 80 m wide. The swimmer aims upstream to land directly opposite.

Find the crossing time.

Organize the givens & assumptions
  • swim speed = 5 m/s
  • current = 3 m/s
  • width = 80 m

Uniform 3 m/s current; swimmer maintains 5 m/s relative to water; banks straight and parallel.

  1. A20 s20\ \mathrm s
  2. B16 s16\ \mathrm s
  3. C10 s10\ \mathrm s
  4. D40 s40\ \mathrm s

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