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A flat mirror revolves at a constant angular velocity making n = 0.4 revolutions per second. With what velocity (in m s - 1 ) will a light spot move along a spherical screen with a radius of 15 m , if the mirror is at the centre of curvature of the screen?

Options

  1. A37.7
  2. B60.3
  3. C68.7
  4. D75.4

Correct answer

D. 75.4

Step-by-step solution

∵ Angular velocity of the mirror = 0.4   r e v   s - 1 = 0.4 × 2 π = 0.8 π   r a d   s - 1 ∴ Angular velocity of the reflected ray = 2 × 0.8 π = 1.6 π   ra d   s - 1 Hence, the velocity of light spot over the screen v = r ω = 15 × 1.6 π = 75.4   m   s - 1

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