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 rev / sec . The light reflected by the mirror is received on

Question

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 $9/ π rev / sec$ . 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 37° find the speed of the spot (a point) on the wall (in km/s).

TestHub · Accepted Answer

Mirror angular speed: ω = 2 π f = 18 rad/s, so the reflected ray rotates at 2 ω = 36 rad/s. With 37° incidence from the normal, the reflected ray makes 5 3 ∘ with the horizontal, so cos 5 3 ∘ = 0.6 . Spot speed at d = 10 m: v = c o s 2 5 3 ∘ 2 ω d ​ = 0.36 36 × 10 ​ = 1000 m/s = 1 km/s. Answer: 1.

Physics - Geometrical Optics Question with Solution | TestHub

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