Question

At an accident scene on a level road, investigators measure a car's skid mark to be 70 m long. It was a rainy day and the coefficient of friction was estimated to be 0.36.(a) Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes.(b) Why does the car's mass not matter? (i) Since both the change in kinetic energy and the work done by friction are proportional to the mass. The mass cancels out of the equation. (ii) Since the work done by friction does not depend on mass. (iii) Since the change in kinetic energy and the work done by friction do not depend on mass.

Answer 1

a) speed of the car = 22.22 m /s

b) ( i )

Step-by-step explanation:

Negative work done by friction will be equal to reduction in kinetic energy of the car.

Frictional force = μ R = μ mg

work done by it = μ mg x 70 m.

Change in kinetic energy = 1/2 m v²

So , μ mg x 70 = 1/2 m v² ------------- ( 1 )

v = √2 x μ x 70 x g

= √2 x .36 x 70 x 9.8

22.22 m/s

As we have seen that m cancels out on both side of equation no ( 1 )