Q. A point object is moving on the principal axis of a concave mirror focal length $24\ cm$ towards the mirror. When it is at a distance of $60cm$ from the mirror, its velocity is $9cm/sec$. What is the velocity of the image at that instant
A) $5cm/sec$ towards the mirror
B) $4cm/sec$ towards the mirror
C) $4cm/sec$ away from the mirror
D) $9cm/sec$ away from the mirror
Explanation
(c) $v_{i} = - \left( \frac{f}{f - u} \right)^{2}.v_{o} = - \left( \frac{- 24}{- 24 - ( - 60)} \right)^{2} \times 9 = - 4\ cm/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.