Question

A car moving along a straight highway with a speed of 72 km/h is broughtto a stop within a distance of 100 m. what is the retardation of the car and how long does it take for the car to stop?

Answer 1

${v}^{2} - {u}^{2} = 2as$
where final velocity=v=0 ,
initial velocity=72kmph=72×5/18=20m/s ,
s is total distance travelled=100m .
$= >{ 0}^{2} - {(20)}^{2} = 2(a)(100)$
=> -400 =200a => a= -2m/s^2 .
v=u+at => 0=20+(-2)t => 20=2t=> t =10 seconds .
So the retardation of the car is 2m/s^2and it takes 10 seconds to stop .Hope it helps you...