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
4m/s2
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B
4.4m/s2
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C
3m/s2
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D
5m/s2
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Solution
The correct option is D5m/s2
By the time he reacts, he travels a distance of 8m. So, he is 40 m away from the car. v20−02=2as⇒202=2×a×40 ⇒a=v2o2s=20×202×40=5m/s2