A 60-kg square and a 90-kg square box was thrown out from an airplane at an altitude of 6000 m, both falling in the flat position. The surface dimension of the boxes are 2 meter by 2 meter in flat position. Calculate their terminal velocities. How long will it take for each box to reach the ground (assuming the time to reach terminal velocity is small)

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.