JEE MAIN - Physics (2020 - 3rd September Evening Slot - No. 4)
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 cms–1, the speed
(in cms–1) with which image moves at that instant is ____.
Answer
1
Explanation
VI = Velocity of image with respect to mirror
V0 = Velocity of object with respect to mirror
$$|\overrightarrow {{V_I}}| = |- {{{v^2}} \over {{u^2}}}\overrightarrow {{V_0}} |$$
$$ = | - {{10 \times 10} \over {30 \times 30}} \times 9|$$
$$ = 1$$ cm/s
V0 = Velocity of object with respect to mirror
$$|\overrightarrow {{V_I}}| = |- {{{v^2}} \over {{u^2}}}\overrightarrow {{V_0}} |$$
$$ = | - {{10 \times 10} \over {30 \times 30}} \times 9|$$
$$ = 1$$ cm/s
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