An object is moving towards a concave mirror of focal length 24 cm. When it is at a distance of 60 cm from the mirror, its speed is `9 cm//s`. The speed of its image at that instant , is

Options

A. 4 cm/s towards the mirror
B. 9 cm/s towards the mirror
C. 4 cm/s away from the mirror
D. 9 cm/s away from the mirror

Answer

C

Explanation

`1/24=1/60+1/v,` now `1/v^(2)xx(dv)/(dt)=(-1)/(-u^(2))xx(du)/(dt)`