Question

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
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 1

Correct Answer - C
`(v_i)/(v_0)=-((f)/(u-f))^2=-[(-24)/(-60-(-24))]^2`
`=-[(-24)/(-36)]^2=-(4)/(9)`
`(v_i)/(9)=-(4)/(9)impliesv_i=-4(cm)/(sec)`
`-ve` sign shows, as object is moving towards mirror, its image moves away mirror.