A car, starting from rest, accelerates at a constant rate of 5 ms–2 for some time. It then retards at a constant rate of 10 ms–2 and finally comes to rest. If the total taken is 6 s, What is the maximum speed attained by the car? 



Correct option is

20 ms–1


Let t1 be the time during which the car has an acceleration a1 = 5 ms–2and t2 be the time during which the car has a deceleration a2 = –10 ms–2. Since the car starts from rest, the maximum speed attained by the car . For time interval, this v is the initial speed and the final speed is zero. Therefore,   






                  = 2  





          t1 = 4 s and t1 = 2 s.   




             = 20 ms–1.




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