Find the average frictional force needed to stop a car weighing 500 kg in a distance of 25 m if the initial speed is 72 km/h.

Explanation

Here, `F=?, m=500kg, s=25m, v=0, u=72km//h=(72xx1000)/(60xx60)m//s=20m//s`
According to word energy principle, `W =`change of K.E. of the body
`Fs=(1)/(2)m(v^(2)-u^(2))`
`Fxx25=(1)/(2)xx500(0-20^(2))=-(500xx400)/(2)`
`F=(500xx200)/(25)=-4000N :.` Average frictional force `=400N`