Question

At an accident scene on a level road, investigators measure a car’s skid mark to be 111 m long. It was a rainy day and the coefficient of friction was estimated to be 0.41. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. Answer: _________ m/s (round to the nearest tenth)

Answer 1

The initial speed of the car is given by the formula:

$v=\sqrt{2\mu gd}$

The car's skid mark is 111m long and the coefficient of friction is 0.41.

Then, replace d=111m, g=9.8m/s^2 and μ=0.41 to find the initial speed of the car:

$v=\sqrt{2(0.41)(9.8\frac{m}{s^2})(111m)}=29.866...\frac{m}{s}\approx29.9\frac{m}{s}$

Therefore, the initial speed of the car was approximately 29.9m/s.