Assume that a car is able to stop with a retardation of 8m/s2 and that a driver can react to an emergency in 0.5sec. Calculate the overall stopping distance of the car for a speed of 72km/hr of the car
A
25m
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B
10m
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C
35m
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D
30m
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Solution
The correct option is C35m Given, reaction time of driver t=0.5sec
retardation of the car 8m/s2 and initial velocity of the car u=72km/hr=20m/s
Distance covered by the car before application of brake S1=20t=20×0.5=10m
Now, car begins to move with the retardation
So, distance covered by car before coming to rest is v2−u2=2as⇒02−202=−2×8×S2 S2=40016=25m ∴ Overall stopping distance of the car is S=S1+S2=10+25=35m