Aparallel-plate capacitor having circular plates of radius r and separation d is held at a fixed potential difference by a battery. if the plates are moved closer together while they are held at the same potential difference
a. the amount of charge on each of them will increase.
b. the amount of charge on each of them will decrease.
c. the amount of charge on each of them will stay the same.
d. the energy stored in the capacitor increases.

C= relative permittivity X permittivity of free space X a/d 

Q= C/V (where Q is charge and V is voltage)

Since C  increases so does the amount of charge on the plates. The stored energy also increases because E= 1/2 CV^2

A and D are correct.

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