1.

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» m = 100 kg 
 V = 0 
 u = 30 m/s
 s = 50 m 
F = ?
W = ?
\frac{1}{2} mv^2 - \frac{1}{2} mu^2WORK done = 
\frac{1}{2} *100 * (0)^2 - \frac{1}{2} * 100 * (30)^2               = 
50 * 0 - * 50 * 900               = 
   W          = - 45000 J

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


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