A coconut falls out of a tree 12 m above the ground and hits a bystander 3 m tall on the top of the head. If the mass of the coconut is 2.0 kg, calculate the potential energy of the coconut relative to the ground while it is still in the tree.

Two 2.0-cm-diameter disks face each other, 1.0 mm apart. they are charged to ±10 nc. what is the electric field strength between the disks? a proton is shot from the negative disk toward the positive disk. what launch speed must the proton have to just barely reach the positive disk?