A man on the top of a vertical tower observes a car moving at a uniform speed towards the tower on a…

A man on the top of a vertical tower observes a car moving at a uniform speed towards the tower on a horizontal road. If it takes 18 min for the angle of depression of the car to change from 30° to 45°, then the time taken (in min) by the car to reach the foot of the tower is
  1. 923-1
  2. 181+3
  3. 183-1
  4. 91+3

Solution



Let length of tower be h.

⇒AC′=AB=h

And AC=ABcot30°=3h

⇒CC′=3-1h

Time taken by car form C C'=18 min

⇒Time take by car to reach the foot of the tower

=183-1 min

=93+1 min

Asked in: JEE Main 2018 (16 Apr Online)

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