Question

A point object 'O' is at the centre of curvature of a concave mirror. The mirror starts to move with speed u, in a direction perpendicular to the principal axis. Then the initial velocity of the image is :

(A)  2u, in the direction opposite to that of mirror's velocity

(B)  2u, in the direction same as that of mirror's velocity 

(C)  Zero

(D)  u, in the direction same as that of mirror's velocity

Answer 1

Correct option (B) 2u, in the direction same as that of mirror's velocity

Explanation :

m =  - V/u = h₁/h0

If object is placed at centre of convature

|V| = |u|

|h_I| = + | h₀|

d|h₁| = +h_o||

d|h₁|/dt  = d|h_o|/dt

d|h₁|/dt = velocity of image wrst mirror, ⟂ to primapal axis 

d|h₀|/dt = velocity of object worst mirro, ⟂ to priampal axis

V_I  –  u = u

V_I  =  2u