An observer is standing at a point O, at a distance of $$100$$ cm from a convex lens of focal length $$50$$ cm. A plane mirror is placed behind the lens at a distance of $$150$$ cm from lens. The magnitude of velocity of her own image as seen by the observer, at the moment when the mirror just starts moving with a velocity of $$10$$ $$cm/s$$.

Question

Infinity Learn · Accepted Answer

V→$$I=2V$$→m−V→$$0$$⇒   V→$$I=2V$$→m∴  velocity of image in the plane mirror will be $$20$$ $$cm/s$$ in the direction of motion of mirror.First refraction at lens, Image is formed at $$I1f=1v$$−$$1u$$​⇒$$150=1v$$−$$1$$−$$100$$​⇒$$v=100Plane$$ Mirror will form image at I'This I' will behave as object for, $$2nd$$ refraction in lens.$$u=$$−$$200cm1f=1v$$−$$1u$$⇒$$150=1v$$−$$1$$−$$200$$⇒$$v=2003$$∴$$dVdt=v2u2dudt=200322002dudt=209cm/s$$

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