Question

A rule states that the friction between dry concrete and a sliding car's tyre is equal to nine-tenth of the car's weight. If the skid marks left by a car coming to rest are 20 m long, how fast was the car going before the brakes were applied?

Answer 1

Answer:

since the frictional force is 0.9mg the retarding acceleration achieved will be 0.9g when brakes are applied. The skid mark distance represents the distance travelled when brakes were applied till the time the car stops completely. Hence this distance is 0.2