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JAMB Physics 1983 Question 10

Question 10

Sound

A ship travelling towards a cliff receives the echo of its whistle after 3.5 seconds. A short while later, it receives the echo after 2.5 seconds. If the speed of sound in air under the prevailing conditions is 250 m s−1, how much closer is the ship to the cliff?

  1. A.10 m
  2. B.125 m
  3. C.175 m
  4. D.350 m
  5. E.1,000 m.
Show the answer and explanation

Answer: B (125 m)

Explanation

Distance = speed × (echo time ÷ 2). First 250 × 1.75 = 437.5 m, then 250 × 1.25 = 312.5 m. The ship is 125 m closer.