Question

A car was moving at the speed of 90 km/hr on seeinh a baby 20m ahead on the road , the driver jammed on the brakes and it comes to rest at a distance of 15m .Calculate it's retardation and time taken by the car to come to state of rest​

Answer 1

Explanation:

Given : initial velocity = 90km/h = 90 × 5/18 = 25m/s

final velocity = 0

distance covered = 15m

using position velocity relation

2as = v²-u²

2×a×15 = 0²-(25)²

30a = -625

a = -625/30 = -20.83 m/s²

As we can see that acceleration is negative

So retardation =20.83m/s²

For time

acceleration = change in velocity/time

-625/30 = v-u/t

-625/30 = 0-25/t

t = -25×30/-625

t = 30/25

t = 1.2 sec