Question

1)A bus ruining at a speed of 18 km/h is stopped in 2.5s by applying brakes. calculate the retardation produced.
2)Find the initial velocity of a car which is stopped in 20 seconds by applying brakes.The retardation due to brakes is 2.5m/s^2

Answer 1

1) u=18 km/h=18*1000/60*60=5 m/s
v=0 m/s
t=2.5 s
a=(v-u)/t
=0-5/2.5=-50/25 = -2 m/s2
Retardation is 2 m/s2

2) t=20 s
v=0 m/s
a= -2.5 m/s2
a=(v-u)/t
-2.5 = 0-u/20
-50=0-u
u=50 m/s