Question

A point object is moving along principal axis of a concave mirror with uniform velocity towards pole. Initially the object is at infinite distance from pole on right side of the mirror as shown. Before the object collides with mirror, the number of times at which the distance between object and its image is 40 cm are.

(A) one time 

(B) two times 

(C) three times 

(D) Data insufficient

Answer 1

Correct option: (C) three times

Explanation:

As the object moves from infinity to centre of curvature, the distance between object and image reduces from infinity to zero. 

As the object moves from centre of curvature to focus, the distance between object and image increases from zero to infinity.

As the object moves from focus to pole, the distance between object and its image reduces from infinity to zero. Hence the distance between object and its image shall be 40 cm three times.