It is desired to photograph the image of an object placed at a distance of $3\;m$ from a plane mirror. The camera,which is at a distance of $4.5\;m$ from the mirror,should be focused for a distance of......$m$.

$A$ person runs with a speed $u$ towards a bicycle moving away from him with speed $v$. The person approaches his image in the mirror fixed at the rear of the bicycle with a speed of:

Two plane mirrors are inclined at an angle of $72^{\circ}$. The number of images of a point object placed between them will be

$A$ boy of height $1.5\, m$ with his eye level at $1.4\, m$ stands before a plane mirror of length $0.75\, m$ fixed on the wall. The height of the lower edge of the mirror above the floor is $0.8\, m$. Then:

$A$ man has a height of $180\, cm$ and his eyes are $10\, cm$ below the top of his head. He uses a plane mirror placed $1\, m$ away to see his full height from head to toe. What is the minimum required height of the plane mirror in $cm$?

Two long plane mirrors $M_1$ and $M_2$ are kept inclined to each other. The angle between reflecting surfaces is $40^o$. $A$ light ray strikes mirror $M_1$ at an angle of $30^o$ with the normal. The maximum number of reflections the ray will undergo is: