A 0.250kg mass book falls from the second floor window. During the fall the book opens, so the friction with the air increases. After a 7.0 m fall, it hits the ground at 7.5 m / s.
What is the average value of the friction force?

Materials will have different energies associated with the electrons inside them. this is related to how strongly bound they are by their work function. if we sandwich a material with a very low energy between two materials with a high energy, we create a trap for an electron. if this trap is very narrow in one direction in comparison to the others, this is approximately a 1-dimensional box that confines the electron. what is the lowest energy of an electron in the box if the thinnest direction across the materials is 4.81 nm?