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A car is fitted with a convex side-view mirror of focal length 20 ~cm . A second car 2.8 ~m behind the first car is overtaking the first car at relative speed of 15 ~m / s . The speed of the image of the second car as seen in the mirror of the first one is :

Options

  1. A1 15 ~m / s
  2. B10 ~m / s
  3. C15 ~m / s
  4. D1 10 ~m / s

Correct answer

A. 1 15 ~m / s

Step-by-step solution

1 v + 1 u = 1 f - 1 v^2 d v d t - 1 u^2 d u d t =0 d v d t =- v^2 u^2 ( d u d t )f=20 ~cm 1 u + 1 -280 = 1 20 v= 280 15 ~cm v₁=- ( 280 15 280 )^2 15= 1 15 ~m / s

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