A man moves towards a plane mirror with a velocity $v$ in a direction making an angle $\theta$ with the normal to the mirror. The magnitude of the velocity of the image relative to man normal to mirror will be

A virtual image three times the size of the object is obtained with a concave mirror of radius of curvature $36 \mathrm{cm}$. The distance of the object from the mirror is

A glass prism $(\mu =1.5)$ is dipped in water $(\mu =4/3)$ as shown in figure. A light ray is incident nromally on the surface AB. It reaches the surface BC after totally reflected, if

A point object is placed at a distance of $20 \mathrm{cm}$ from a thin plano-convex lens of focal length $15 \mathrm{cm}$. If the $B$ plane surface is silvered, the image will from at