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State PCS PYQPrelims 2024

UPPCS · Question 71

A bus covers the first half of a certain distance with speed v1 and the second half with a speed v2. The average speed during the whole journey is:

  1. v1v2 / (v1 + v2)
  2. 2v1v2 / (v1 + v2)
  3. (v1 + v2) / 2
  4. sqrt(v1v2)
Show answer & explanation

Answer: (B) 2v1v2 / (v1 + v2)

Explanation

Average speed = total distance / total time = 2d / (d/v1 + d/v2) = 2v1v2/(v1 + v2), the harmonic mean.