Determine the time required for the car to stop & coeff. of kinetic friction between the tires & the road.

Initial KE of motorist $= (1/2) m 25^2 $

Final KE of motorist = 0

Energy lost to frictional force $= µmgs = µmg(100) $

Now, applying work energy theorem

$0 - (1/2)m 253 = - µmg(100) \\ µ = 0.3185 \\ Using, v2 = u2 + 2as \\ 0 = 252 + 2a(100) \\ a = -3.125 m/s^2 $

Now, using $v= u + at \\ 0 = 25 - 3.125(t) \\ t = 8 sec$

Time required to stop the car is 8 sec & coefficient of friction between road & tyres is $0.3185$