# Kinematics

1) A policeman investigating an accident measures the skid marks left by a car. He determines that the distance between the point that the driver slammed on the brakes and the point where the car came to a stop was 34.0 m. From a reference manual he determines that the coefficient of kinetic friction between the tires and the road under the prevailing conditions was 0.300. How fast was the car going when the driver applied the brakes? (This car was not equipped with anti-lock brakes.)

10.7 m/s

14.1 m/s

21.4 m/s

32.9 m/s

https://brainmass.com/physics/velocity/kinematics-fast-car-going-110443

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A policeman investigating an accident measures the skid marks left by a car. He determines that the distance between the point that the driver slammed on the brakes and the point where the car came to a stop was 34.0 m. From a reference manual he determines that the coefficient of kinetic friction between the tires and the road under the prevailing conditions was 0.300. How fast was the car going when the driver applied the brakes? (This car was not equipped with anti-lock brakes.)

10.7 m/s

14.1 m/s

21.4 m/s

32.9 m/s

Answer: 14.1 m/s

Uniformly accelerated motion

V0= initial velocity

Vf= final velocity

a= acceleration

delta s= displacement

Equation used:

Vf ^2 = Vi ^2 + 2 a delta s

V0= initial velocity = ? m/s

Vf= final velocity = 0 m/s

delta s= displacement = 34 m

Mu = 0.3

g= 9.81 m/s^2

a=Mu g= 2.94 m/s^2

Vi=square root of (2 a delta s) 14.1 m/s

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