I am looking over my review and a few questions I am lost on: 1. The disk shaped head of a pin is 1.0mm in diameter. What is the best estimate for the number of atoms on the top layer of the pinhead. -I have no idea where to begin with this... any ideas? 2.How does density fit in when the absolute temperature of a sample of monatomic ideal gas is doubled at constant volume? - pV=nRT , Where does the density fit in? 3. WHat is the KE of a rock just before it hits the ground? - I used the conservation of energy and didn't come up with the right answer... the correct answer is KEi + mgh... I don't know how to derive this though? Thank ya.