Question

A girl of heigh 90 cm is walking away from the base of a lamp-post at a speed of 1.2 m/sec. If the lamp is 3.6 m above the ground, find the length of her shadow after 4 seconds.

Answer 1

It is given that, girl height, speed and height of lamp.

We have to find the length of her shadow after

Let be the lamp post and be the girl.

Suppose is the length of her shadow.
Let DE = x

And

Now in and we have

and

So by similarly criterion

$$\begin{gathered} \frac{BE}{DE}=\frac{AB}{CD} \\ \frac{4.8+x}{x}=\frac{3.6}{0.9}=4 \\ \Rightarrow 3x=4.8 \\ \Rightarrow x=1.6 \end{gathered}$$

Hence the length of her shadow after is 1.6 m.