Why is a cell phone more likely to break when dropped from a higher height than a lower one?

How does the space charge width change with forward and reverse bias? also, calculate the space charge width for a reverse bias of 4v on a silicon pn junction at t = 300k and doping concentrations of na = 5x1015cm-3 , nd = 5x 1016 cm-3 .

Consider a system to be two train cars traveling toward each other. what is the total momentum of the system before the train cars collide?   kg • what must the total momentum of the system be after the train cars collide?   kg •  

What happens to an isotope during radioactive decay?