Question

The ratio of length of man and length of his shadow is 9:5 . find the height of his shadow , if height of man is 720 cm​

Answer 1

Answer:

Let AB be the lamp post

and let MN be the man of height 2m

and let AM=lmeter.

and MS is the shadow of the man.

Let length of shadow MS=s

Given: Man walks at speed of 5kmph

∴ dt/dl =5kmph

We need to find rate at which the length of his

shadow increases= dt/ds

In △ASB,tanθ= AS/AB = l+s6....(1)

In △MSN,tanθ= MS/MN = s2 ....(2)

From (1) and (2)

l+s6 = s2

⇒6s=2l+2s

⇒4s=2l or l=2sdt/dl =2 dtds5=2 dtds since given that dt/dl =5kmph

∴ dt/ds = 25 kmph=2.5kmph

Step-by-step explanation:

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