A factory worker pushes horizontally a 30-kg crate to a distance of 4.5 m along a
level floor at a constant velocity. The coefficient of kinetic friction between the
crate and the floor is 0.25.

a. What magnitude of force must the worker apply?
b. How much work is done on the crate by this force?
c. How much work is done on the crate by the friction force?
d. How much work is done by the normal force? By the gravity?
e. What is the net work done on the crate?