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A man is walking towards a vertical pill...

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 `30^0` . 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`60^0` . Then the time taken (in minutes) by him, from B to reach the pillar, is : (1) 6 (2) 10 (3) 20 (4) 5

A

6

B

10

C

20

D

15

Text Solution

Verified by Experts

The correct Answer is:
D
Let v metre/minute be the speed of the man and PQ by pillar of height h metres. It is given that AB=10v. `BQ=v_1`. In triangles AQP and BQP , we have
tan `30^@=h/(10v+BQ)` and tan `60^@=h/(BQ)`

`rArr sqrt3h=10v +BQ`
`rArr BQ=5v rArr vt =5u rArr t =5`
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OBJECTIVE RD SHARMA-HEIGHTS AND DISTANCES-Exercise
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