Question

A car starts from rest and accelerates at uniform rate of 5m/s2 for sometime, then moves with constant speed for some time and retards at the same uniform rate and come to rest. Total time for the journey is 25s and average speed for the journey is 20m/s. How long does the car move with constant speed?.......

Answer 1

Answer:

Avg speed × total times = total distance

20×25=500

Since acceleration in the 1st interval is same as deceleration in the 3rd interval and deceleration is from the same velocity achieved after acceleration, t1 =t3

S1 = 1/2 * 5t1^2

S2 =( 5t1) t2

(5t 1 )×t 3 − 1/2 ×5×t 1/2 =(5t 1 )×t 1 −1/2 ×5×t

Solving (1 ) and (2) ⇒t

=15sec

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