Question

James Stewart, 2002 Motorcross/Supercross Rookie of the Year, is leading a race when he runs out of gas near the finish line. He is moving at 16 m/s when he enters a section of the course covered with sand where the effective coefficient of friction is 0.90. Will he be able to coast through this 15-m-long section to the finish line at the end? If yes, What is his speed at the finish line?

Answer 1

We are given the coefficient of friction which is:
Cf = 0.90
The acceleration based on this would be:
a = -Cf * g 
a = -0.90 * (9.81 m/s^2)
a = -8.83 m/s^2
Calculate the distance at his total stop v = 0 using the formula:
v^2 = vo^2 + 2ad
where v is final velocity = 0, vo is initial velocity = 16, d is distance
0 = 16^2 + 2 (-8.83) d
d = 14.5 m
So he is short by 0.5 m, he does not reach the finish line