Question

A man of height h walks in a straight path towards a lamp post of height H, with a uniform velocity u. The velocity of the edge of his shadow on the ground will be

(1) (H/H+h)u

(2) (H/H-h)u

(3) (H+h/H)u

(4) (H+h/H-h)u

Answer 1

(2) (H/H-h)u

Suppose x is the length of the shadow. When the man is at d distance from the pole, as shown in Fig. If he takes t seconds to reach the pole, the edge of his shadow will also reach the pole in the same time t

The distance travelled by the edge of the shadow, in t seconds, is equal to x + d. The velocity of the edge, v is