Question

A man is running towards a plane mirror at the rate of $2m/s$. With what speed is he approaching his own image?

Answer 1

Explanation

1. A plane mirror has an infinite focal length.
2. As a result, the object's distance from the mirror is equal to the mirror's distance from the image.
3. Thus, if the man moves $2m/s$ toward the mirror, the mirror image will also move $2m/s$ towards him.
4. As a result, his speed toward the mirror plus the speed of the mirror image toward him is $2+2=4m/s.$

Hence, the speed at which he approaches his own image is $4m/s$.