Question

A motor cyclist travelling at 12m/s decelerates at 3m/s square
a) how long does he take to come to a rest
b) how far does he travel in coming to rest

Answer 1

average speed during stop = 12/2 = 6

v = Vi - a t
0 = 12 - 3 t to stop (get v = 0)
so
t = 12/3 = 4 seconds to stop

distance = average speed * time
= 6 * 4
= 24 meters