A stationary concave mirror forms a real image. An object approaches at 2 cm/s while the image recedes at 18 cm/s. If object-image separation is 40 cm, find the object distance in centimetres.
Physics · Geometrical optics · spherical mirror
JEE Mains NEET

Question

A stationary concave mirror forms a real image. An object approaches at 2 cm/s while the image recedes at 18 cm/s. If object-image separation is 40 cm, find the object distance in centimetres.

G1 Physics · Accepted Answer

Speed ratio=9 gives |m|=3, so v=3u. Separation=v−u=2u=40, hence u=20 cm.