Q. 104.4( 8 Votes )

# A give of height 90 cm is walking away from the base of a lamp – post at a speed of 1.2 m/s. If the lamp is at a height of 3.6 m above the ground, find the length of her shadow after 4 seconds.

Answer :

The speed of give = 1.2 ms ^{– 1}

Time taken = 4 seconds

Distance = speed × time taken

In 4 seconds, the distance walked is 1.2×4 = 4.8 m.

As both the lamp post and the give are perpendicular to the ground, they make the following similar triangles.

In ΔBDE & ΔBAC,

∠B = ∠B |common angle

DE||AC

∠BDE = ∠BAC

ΔBDE~ΔBAC by AA Similarity Rule

4x = x + 4.8

⇒ x = 1.6 m

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