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# CBSE Class 12-science Answered

A girl whose height is 160 cm is walking with a speed of 4 m/min away from a lamppost, which is 6.4 m high. Now, her shadow is being formed which is increasing as she moves away. Find out the rate at which the shadow is increasing.
Asked by Topperlearning User | 05 Aug, 2014, 01:49: PM

Here let us take 'x' be the distance covered by the girl in time t.

Then

If 'y' is length of shadow in time 't' min then the rate at which the

Length of shadow is increasing is  which is required.

From the figure it is clear that

which means

Now differentiating the above equation with respect to it, we get

But it is given,

This means that the shadow is increasing at the rate of 12m/min.

Answered by | 05 Aug, 2014, 03:49: PM

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