When the 20 kg box to the right is pulled with a force of 100 N, it just starts to move. What is the value of the coefficient of static friction,
uS? (Assume g=10m/s2)

What is the things about?

W= fd
where f is an applied force and d is the distance over which it is applied. when a parachuting skydiver is at constant velocity, he is experiencing "terminal velocity", the point at which his acceleration down is canceled out by air resistance. that means that the resisting force of the air is equal to his weight, but in the opposite direction. with this, we can solve for the work done by the force.
w = fd
w = (92.0)(9.81 m/s^2) (325)
w= 2.93 x 10^5 j
the value for work in this case is positive because it is pushing up on the skydiver, who has a downward force of gravity.
therefore the answer is 2.93 x 10^5 j

If your workout exceeds an hour you should substitute "a sports drink" for water.hope my answer has you : )