Click on the reset button, and stack one 50kg. crate on top of the other, so that the total mass is 100kg. The Friction should be set to halfway between None and Lots. Adjust the Applied Force (force exerted) slowly, and determine when the crates begin accelerating. What is the minimum force that must be exerted on the crates so that they accelerate?

The correct choice is c

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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