A car of length 3 m moves at a constant velocity 36 km/hr. A man wants to take a photo of side view of the car. The size of the image of the car is 1.5 cm long. The time of exposure needed for the car to get a clear picture, if the image should not move more than 0.1 mm, is…….

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$1 .5 \times 10^{- 3} S$

$2 \times 10^{- 3} S$

$2 .8 \times 10^{- 3} S$

$3 \times 10^{- 3} S$

answer is D.

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Detailed Solution

Magnification of the image $= \frac{1 .5 \times 10^{- 2}}{3} = 5 \times 10^{- 3}$
Velocity of the image = m × velocity of the object
$= 5 \times 10^{- 3} \times 10 = 5 \times 10^{- 2} m / s Distance travelled by the image = 0 .1 \times 10^{- 3} m time = \frac{0 .1 \times 10^{- 3}}{5 \times 10^{- 2}} = 2 \times 10^{- 3} s$