Question

A 1.5 m tall boy is walking away from the base of a lamp post which is 12 m high, at the speed of 2.5 m/sec. Find the length of his shadow after 3 seconds.

Answer 1

Distance = S × t

= 2.5 × 3

= 7.5 m

In ΔABE and ΔCDE

∠B = ∠D  .....(Each 90°)

∠E = ∠E   .....(Common)

ΔАВЕ ~ ΔCDE  ....(By AA similarity)

`(AB)/(CD) = (BE)/(DE)`

`12/1.5 = (7.5 + x)/x`

8 = `(7.5 + x)/x`

8x = 7.5 + x

7x = 7.5

x = `7.5/7`

x = `75/70`

x = `15/14` m

∵ x = `15/14` m or 1.07 m

The length of his shadow is 1.07 m.