Question

calculate the retardation produced by the brakes also
calculate the distance covered in those 5 second

Answer 1

a= (v-u)/t
a = (20-30)/5
a=-10/5
a=-2m/s^2

distance travelled in 5 sec
$s = ut + (1 \div 2)at {}^{2}$
s = 30×5+0.5(-2)×5×5
s = 150+(-1×25)
s = 150-25
s = 125m