Question
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.
