Almost Hit By a Car!
A man drive his car with the speed 72 km/h, accidentally he sees a Boy in the middle of the road 48 meter from his car. The Driver needs 0.36 second to activate the brakes and when the brakes has been activated it gives 5 m/
deceleration. Is the Boy got hit by the car?
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1 solution
By the third equation of motion v 2 − u 2 = 2 × a × S we have v = 0 , u = 2 0 m s − 1 , a = 5 m s − 2 , S = ? Solving for S here, we have S = 4 0 m Now before the brakes come into play, the car moves on 72 km/h, i.e. 20 m/s for 0.36 second, covering 2 0 m s − 1 × 0 . 3 6 s = 7 . 2 m Removing 7.2 m from the given 48 m, we still have a distance greater than 40 m, therefore the boy is NOT hit.