A 25-kg box slides, from rest, down a 9.0-m-long incline that makes an angle of 15° with the horizontal. The speed of the box when it reaches the bottom of the incline is 2.4 m/s.
a. What is the coefficient of kinetic friction between the box and the surface of the incline?
b. How much work is done on the box by the force of friction?
c. What is the change in the potential energy of the box?