Question

A point source of light S is placed at a distance 10 cm infront of the centre of a mirror of width 20 cm suspended vertically on a wall. A man walks with a speed 10 cm/s infront of the mirror along a line parallel to the mirror at a distance 20 cm from it as shown in figure. Find the maximum time during which he can see the image of the source S in the mirror :

Answer 1

Distance= Speed* Time

He can see S only when he is in front of the mirror.

so distance = 20 cm

t = d/sp

t = 20 * 10

t = 200 sec

He'll be able to see it for 200 sec

Hope it helps.....

Answer 2

Explanation:

ANSWER IS 6SECONDS. FIRST FIND LENGTH OF PATH TRAVELLED BY THE MAN. ITS VALUE IS 120m.

Hence,

S=V(T)

120=10(T)

T=12s

But he can't see the image when he is above and below mirror height.

Hence ,

time t = 6 s