The student exerts a force of 40 N on the crate, the force is directed at an angle 20 degrees below the horizontal. This results in the crate moving at a constant velocity for a distance 15 m.

We have to determine the coefficient of kinetic friction. The horizontal component of the force applied by the student on the crate is 40*cos 20. The force of friction is n*20*9.8 where n is the coefficient of kinetic friction.

n*20*9.8 = 40*cos 20

=> n = 40*cos 20/(20*9.8)

=> n = 0.1917

The coefficient of kinetic friction is 0.1917.

The work done by the student in moving the crate is 40*cos 20*15 = 563.81 J. The work done by the force of friction is also 563.81 J.

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