A man is walking towards a vertical pillar in a straight path, at a uniform speed. At a certain point A on…

A man is walking towards a vertical pillar in a straight path, at a uniform speed. At a certain point A on the path, he observes that the angle of elevation of the top of the pillar is 30°.  After walking for 10 minutes from A in the same direction, at a point B, he observes that the angle of elevation of the top of the pillar is 60° . Then the time taken (in minutes) by him, from B to reach the pillar, is
  1. 20
  2. 5
  3. 6
  4. 10

Solution

ΔQPA :hx+y=tan30°

3h=x+y ......i

ΔQPB :hy=tan60°

h= 3y   ......ii

From equation i & ii, we get

3y=x+y 

y=x2

Speed is uniform

Therefore, distance x walked by him in 10 min.

and distance x2 walked by him in 5 min.

Asked in: JEE Main 2016 (03 Apr)

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