otential difference ΔVΔV exists between the inner and outer surfaces of the membrane of a cell. The inner surface is negative relative to the outer surface. If 2.70×10−20 J2.70×10−20 J of work is required to eject a positive sodium ion (Na+)(Na+) from the interior of the cell, what is the magnitude of the potential difference (in millivolts) between the inner and outer surfaces of the cell?

Aspring has a relaxed length of 33 cm (0.33 m) and its spring stiffness is 6 n/m. you glue a 76 gram block (0.076 kg) to the top of the spring, and push the block down, compressing the spring so its total length is 15 cm. you make sure the block is at rest, then at time t=0 you quickly move your hand away. the block begins to move upward, because the upward force on the block by the spring is greater than the downward force on the block by the earth. calculate y vs. time for the block during a 0.09-second interval after you release the block, by applying the momentum principle in three steps each of 0.03-second duration.