The height of a room is 6m.A person of height 1.5m is standing at the centre of a room.A plane mirror is to be fixed on front wall the minimum vertical lenght of the mirror so that the person can see complete image of his own and the wall behind him?

Answer 1

draw a ray diagram. To see his feet, the base of the mirror must be 1/2 way between the floor and his eyes.
if he can see his feet, he can see the base of the wall behind.
Now to see the top of the wall behind, the top of the mirror must be 1/2 way up from his eyes to the top of the ceiling.

So figure the distance between the base and the top of the mirror.