Let AB is the stature of streetlamp post and CD is the tallness of the man with the end goal that

\[AB\text{ }=\text{ }5\left( 1/3 \right)\text{ }=\text{ }16/3\text{ }m\text{ }and\text{ }CD\text{ }=\text{ }2\text{ }m\]

Let \[BC\text{ }=\text{ }x\] length (the distance of the man from the light post)

What’s more, \[CE\text{ }=\text{ }y\] is the length of the shadow of the man at any moment.

It’s seen from the figure that,

\[\text{ }ABE\text{ }\sim\text{ }\text{ }DCE\]  [by AAA closeness criterion]

Presently, taking proportion of their relating sides, we have

Separating the two sides w.r.t, t, we have

In this way, the length of shadow is diminishing at the pace of 1 m/s.

Presently, let \[u\text{ }=\text{ }x\text{ }+\text{ }y\]

(where, u = distance of the tip of shadow from the light post)

On separating the two sides w.r.t. t, we get

Hence, the tip of the shadow is moving at the pace of m/s towards the light post and the length of shadow diminishing at the pace of \[1\text{ }m/s.\]