Question

A bus decreases its speed from 72km/h in 10 sec. calculate the acceleration of the by?

Answer 1

if it comes to stop then ,
a = (v-u)/t
v = 0
u = 72 km/h
= 20 m/s
t = 10 s
a = (0-20)/10
= - 20/10
= -2 m/s^2

Answer 2

Since here velocity is not given , we assume the speed as velocity .
u=72 km/h=72*5/18 m/s=20 m/s.
Since final velocity is not given , we assume it to be 0.
v=0 , t=10 s.
⇒a=(v-u)/t=(0-20)/10 m/s²
=-20/10 m/s² = -2 m/s².
The bus is accelerating at the rate of -2 m/s².
or it is decelerating  at the rate of 2 m/s².