(Challenge Problem) A worker pulls a 40.0-kg crate with a rope at the 30.0o angle to the horizontal. The coefficient of sliding friction between the crate and the floor is 0.55. If he moves the crate
with a constant velocity a distance of 7.00 m, how much work does the worker do on the crate?
(hint: make 2 equations for 2 unknowns)

The space between two 15-in.-long concentric cylinders is filled with glycerin (viscosity = 8.5 × 10-3 lb·s/ft2). the inner cylinder has a radius of 1 in. and the gap width between cylinders is 0.1 in. determine (a) the torque and (b) the power required to rotate the inner cylinder at 180 rev/min. the outer cylinder is fixed. assume the velocity distribution in the gap to be linear.