Question

An automobile can accelerate or decelerated at a maximum value of `5m//s^(2)` and can attain a maximum speed of `90 km`hr. It it starts from rest. What is the shortest time in which can travel 80 metre. If it is comes to rest at the end of the 80 metre run ?
A. `4 sec`
B. `8 sec`
C. `16 sec`
D. `32 sec`

Answer 1

Correct Answer - B
Automobile will not attain its maximum possible speed in this motion.
`rArr` Automobile will accelerate for first half of motion & deccelerate for another half of motion and attain maximum speed `v = 5t`
so, Area under `v - t` graph gives displacement `= 80 m`
`80 = (1)/(2) xx v x 2t`
`2t = 8 sec`