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A man 2 metres high walks at a uniform s...

A man 2 metres high walks at a uniform speed of 5 km/hr away from a lamp-post 6 metres high. Find the rate at which the length of his shadow increases.

A

5m/h

B

`(5)/(2)(m)/(h)`

C

`(5)/(3)(m)/(h)`

D

`(5)/(4)(m)/(s)`

Text Solution

Verified by Experts

The correct Answer is:
B

`(dy)/(dt)=5,(dx)/(dt)=?`
From figure, `(x)/(2)=(x+y)/(6)implies4x=2yimpliesx=(1)/(2)y`
Hence `(dx)/(dt)=(1)/(2)(dy)/(dt)=(5)/(2)` metre/hour
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