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JEE Advanced2022PhysicsRay OpticsActual

An object and a concave mirror of focal length f = 10 cm both move along the principal axis of the mirror with constant speeds. The object moves with speed V 0 = 15 cm s - 1 towards the mirror with respect to a laboratory frame. The distance between the object and the mirror at a given moment is denoted by u . When u = 30 cm , the speed of the mirror V m is such that the image is instantaneously at rest with respect

Correct answer

0

Step-by-step solution

Magnification expression for concave mirror is given by, m = f f - u = - 10 - 10 - - 30 = - 1 2 For concave mirror, we can write, v i , m = - m 2 v o . m ⇒   v o - v m × m 2 + v i - v m = 0 As given in the question, v i = 0 . Therefore, ⇒   v o - v m × 1 4 = v m ⇒ v o = 5 v m ⇒ v m = v o 5 = 15 5 = 3   cm   s - 1

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