A man runs towards a mirror at a speed +6m/s. If the mirror is at rest, his image will have a velocity (with respect to man)
A
12m/s
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B
−6m/s
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C
6m/s
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D
−12m/s
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Solution
The correct option is D−12m/s
Given that, man velocity (u)=6m/s For a plane mirror, Object distance = image distance ⇒x=x′ Differentiating both sides w.r.t. time, ⇒dxdt=dx′dt ⇒u=u′=6m/s So, object speed = image speed = 6m/s Taking rightwards as +ve direction, velocity of image w.r.t. man is (vi,m) ⇒vi,m=(−u′)−u=−2u=−12m/s Hence, option (d) is the correct answer.