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 28.0 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.)
A) 10.7 m/s
B) 12.8 m/s
C) 21.4 m/s
D) 32.9 m/s
E) 45.7 m/s

Question

Quizplus · Accepted Answer

The equation for the distance traveled by a skidding car is:

d = (v^2)/(2μg)

where d is the distance traveled, v is the initial velocity, μ is the coefficient of kinetic friction, and g is the acceleration due to gravity (9.81 m/s^2).

Plugging in the given values, we get:

28.0 m = (v^2)/(2*0.300*9.81 m/s^2)

Simplifying and solving for v gives:

v = sqrt(2*0.300*9.81 m/s^2*28.0 m) = 12.8 m/s

Therefore, the answer is B) 12.8 m/s.

A Policeman Investigating an Accident Measures the Skid Marks Left