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Question: A car starts moving rectilinearly from rest with 5ms<sup>-2</sup> form sometime, then uniformly and ...

A car starts moving rectilinearly from rest with 5ms-2 form sometime, then uniformly and finally decelerates at 5 ms-2 and come to a stop. The total time of motion equal 25 s. How long does the car move uniformly? Given Vav= 72 km/h during motion.

A

5s

B

10 s

C

15 s

D

20 s

Answer

20 s

Explanation

Solution

Total distance covered = area under v – t graph.

From fig.

20 × 25 = 5t12 + (25 – 2t1) 5t1

or 5t12 – 125 t1 + 500 = 0

or (t1 - 5) (t1- 20) = 0

⇒ t1 = 5s discard t1 = 20 s.