A flat sheet of crown glass has a thickness of 2.6 cm. It is on top of a flat sheet of crystalline quartz that has a thickness of 3.2 cm. Light strikes the crown glass perpendicularly and travels through it and then through the crystalline quartz. In the time it takes the light to travel through the two sheets, how far would it have traveled in a vacuum

Uranium has two naturally occurring isotopes. 238u has a natural abundance of 99.3% and 235u has an abundance of 0.7%. it is the rarer 235u that is needed for nuclear reactors. the isotopes are separated by forming uranium hexafluoride uf6, which is a gas, then allowing it to diffuse through a series of porous membranes. 235uf6 has a slightly larger rms speed than 238uf6 and diffuses slightly faster. many repetitions of this procedure gradually separate the two isotopes. what is the ratio of the rms speed of 235uf6 to that of 238uf6? express your answer to five significant figures.