friction force = -.5 m g
= .5 (9.81) m = -4.9 m
a = F/m = -4.9 m/s^2
average speed during stop = Vi/2
so 60 = (Vi/2)t
120 = Vi t
Vi = 120/t
60 = Vi t - .5(4.9) t^2
60 = 120 - 2.45 t^2
t = 7 seconds
Vi = 120/7 = 17.1 m/s
During the investigation of a traffic accident that occurred in a 25 m/s zone, police find skid marks 60.0 m long corresponding to the distance the car traveled while braking to a halt. They determine that the coefficient of friction between the car's tires and the roadway to be 0.50 for the prevailing conditions. Was the car speeding when it began to slide? Determine the speed of the car when the brakes were applied.
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