Question

At an accident scene on a level road, investigators measure a car's skid mark to be 84 m long. It was a rainy day and the coefficient of friction was estimated to be 0.36.

Answer 1

Explanation:

We know:

KE=12mv2=Fd

KE=

2

1

​

mv

2

=Fd

Where Fd=umgdFd=umgd Thus,

12mv2=umgd

2

1

​

mv

2

=umgd

12v2=ugd

2

1

​

v

2

=ugd

v2=2ugd

v

2

=2ugd

v=2ugd−−−−√

v=

2ugd

​

v=2(0.3)(9.81)(78)−−−−−−−−−−−−−√

v=

2(0.3)(9.81)(78)

​

v=21.4m/s

v=

21.4m/s

​

Part B

The cars mass does not matter because we can see that the mass cancels out from both sides of the equation.