An object is at a distance of 20 m form a convex lens of focal length 0.3m The lens forms an image of the object moves away form the lens at a speed of `5m//s` the speed and direction of the image will be :

Options

A. `1.16xx10^(-3)` m/s towards the lens
B. `2.26xx10^(-3)` m/s away from the lens
C. `0.92xx10^(-3)` m/s away from the lens
D. `3.22xx10^(-3)` m/s towards the lens

Answer

A

Explanation

Since the object is very far from the lens , the image is formed approx, at focus , so,
`m(long)=(+v^2)/u^2=+(0.3/20)^2`
Also , for an object moving along the optic axis :
`V_i=V_0m` (long)
So, `V_i=+5xx(3/200)^3 = +1.16xx10^(-3)` m/s
For lens, image moves in the same direction as object.