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Question

A Driver is driving a car at speed of 72 km/hr on road. He sees a boy on road at a distance of 48 m from him. If his reaction time is 0.4 sec, find minimum retardation required to save the boy.

A
4 m/s2
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B
4.4 m/s2
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C
3 m/s2
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D
5 m/s2
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Solution

The correct option is D 5 m/s2

By the time he reacts, he travels a distance of 8m. So, he is 40 m away from the car.
v2002=2as202=2×a×40
a=v2o2s=20×202×40=5m/s2

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