Asurfer is able to stay on the surfboard as she rides the waves. which explains the force(s) that enable her to do this? a. the force of gravity pulls the surfer into the surfboard with enough force to hold her on the surfboard. b. the surfer exerts a force on the surfboard, and the surfboard exerts a force on the surfer that is equal in magnitude and opposite in direction. c. the forward force of the surfboard's acceleration is balanced by the backward force of the surfer's mass. d. the force of friction between the surfer and the surfboard keeps the two traveling together.

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.