Question

A body moving with 10m/s comes to rest 2sec. Find retardation

Answer 1

final velocity v=0m/s
initial velocity u=10m/s
Time taken to comes to rest is t=2sec
retardation =
$a = \frac{v - u}{t} \\ a = \frac{0 - 10}{2} \\ a = - 5m {s}^{ - 2}$
hence the retardation is -5m/s^2

Answer 2

acceleration=(v2-v1)/t
=(0-10)/2
=-10/5
=-2
so the retardation is +2m/s^2