Question

A motorcycle driven at a speed of 20 m/s when brakes are applied to it bring it to rest in 5s .Find deceleration.

Answer 1

v-u/t=a
hence
v =0
u=20m/s
t=5s
so 0-20/5= -20/5
-5 m/s square

Answer 2

u = 20 m/s , a=?
t = 5s
v = 0m/s
v = u + at
0 = 20 + 5a
-20/5 = a
a = -4 m/s²
negative sign shows that it is deceleration and is acting direction opposite to motion of body.