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A driver of a car travelling at 52km/h applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5s. Another driver going at 3km/h in another car applies his brakes slowly and stops in 10s. On the same graph paper , plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
Asked by Santosh.kumar0317 | 11 Jun, 2019, 01:05: PM
answered-by-expert Expert Answer
Car-1 :-
 
Initial speed = 52 km/h  = 20 m/s
 
if it is stopped in 5 seconds, retardation = u/t = 20/5 = 4 m/s2
 
speed at given time t after aplying break is calculated from ,  v = u - ( a×t ). Graph is shown below
Distance travelled after applying break before coming to rest :-   S = u t - (1/2) a t2  = 20×5 - (1/2)×4×5×5 = 100 - 50 = 50 m
 
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Car-2 :-
 
Initial speed = 3 km/h  = (5/6) m/s
 
if it is stopped in 10 seconds, retardation = u/t = (5/6)/10 = (1/12) m/s2
 
speed at given time t after aplying break is calculated from ,  v = u - ( a×t ). Graph is shown below
 
 
Distance travelled after applying break before coming to rest :-   S = u t - (1/2) a t2  = (5/6)×10 - (1/2)×(1/12)×10×10 = (25/6) m
Answered by Thiyagarajan K | 11 Jun, 2019, 02:29: PM

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