Question

A car is moving in a straight line with speed 18 km/h.It is stopped in 5 s by applying the brakes.find: :.iii)the speed of the car after 2 s of applying the brakes.

Answer 1

initial speed, $u=18km/h=5m/s$
$t=5s$
final speed, $v=0km/h$

velocity of car $t$ seconds after applying the breaks is given by
$v(t)=u+at$

plugin the given values above and find $a$ :
$0=5+a(5)\implies a=-1m/s^2$

therefore the velocity of car as a function of time is
$v(t)=5-t$

plugin $t=2$ for the velocity of car $2$ seconds after applying breaks:
$v(t)=5-2=3m/s=10.8km/h$