Question

A bus running at a speed of 18km/h is stopped in 2.5 sec by applying brakes. Calculate the retardation produced.

Answer 1

initial velocity = 18 km/h = 18×5/18 m/sec
= 5 m/sec
[ km/h = 5/18 m/sec ]

final velocity = zero

acceleration = change in velocity/time
= ( final velocity - intial velocity)/time
= ( 0 - 5)/2.5 = -2 m/s²

so, retardation = 2m/s²

Answer 2

initial speed of bus= 18km/h i.e 5m/s 
time taken by bus to stop after applying brakes=2.5s
final speed of bus=0(because it stops)

so by newtons first equation--> v=u+at 
0=5+a(2.5) 
a= -2m/s²

as retardation is asked then answer will be 2m/s².