Question

A point object is moving along the principal axis of a concave mirror with uniform velocity towards the pole. Initially, the object is at an infinite distance from the pole on the right side of the mirror as shown. Before the object collides with the mirror, the number of times for which the distance between the object and its image is $50\text{cm}$ are

• A. One time
• B. Two times
• C. Three times
• D. More than three times

Answer 1

The correct option is C Three times

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

As the object moves from the 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 changes again from infinity to zero.

Hence, the distance between the object and its image shall be exactly equal to $50\text{cm}$ three times.
Hence, option $\left(c\right)$ is the correct answer.