Q72 / 75 · JEE Main 2020 (03 Sep Shift 2) · Physics

When an object is kept at a distance of $30 cm$ from a concave mirror, the image is formed at a distance of $10 cm$ from the mirror. If the object is moved with a speed of $9 cm s^{- 1}$ , the speed (in $cm s^{- 1}$ ) with which image moves at that instant is

Correct answer: 1

Solution

Velocity of image

$v_{i} = - \frac{v^{2}}{u^{2}} \times v_{0}$

$= - \frac{10^{2}}{30^{2}} (9)$

$= - 1 cm \sec^{- 1}$

Hence, the correct answer is 1.

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