Question

a car weighing100kg and travelling at 30m/s stops at a distance of 50m accelerating uniformaly . what is the force exerted on its brakes ? what is the work done by the brakes ?

Answer 1

m = 100 kg 
 v = 0 
 u = 30 m/s
 s = 50 m 
F = ?
W = ?
work done = $\frac{1}{2} mv^2 - \frac{1}{2} mu^2$
               = $\frac{1}{2} *100 * (0)^2 - \frac{1}{2} * 100 * (30)^2$
              = [tex]50 * 0 -  * 50 * 900 [/tex]
   W          = - 45000 J

$W = F * S$
     $\frac{W}{S} = F$
     $\frac{-45000}{50} = F$
 therefore, F = - 900N 

Answer 2

please see the attach