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A light ray I is incident on a plane mirror M. The mirror is rotated in the direction as shown in the figure by an arrow at frequency 9/π rps. The light reflected by the mirror is received on the wall W at a distance 10 m from the axis of rotation. When the angle of incidence becomes 37º the speed of the spot (a point) on the wall is :

(A)  10 m/s 

(B)  1000 m/s 

(C)  500 m/s

(D)  None of these

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Correct option  (B) 1000 m/s

Explanation :

ω' of reflected light is

ω' = 2(9/π 2π) = 36 rad/sec

V' = Rω' 

Let velocity of spot on wall is

v cos 53º = Rω' 

v = 10/cos 53º x 36/cos 53º = 36 x 25/9 =  1000 rad/sec

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