Students want to build a simple motor to demonstrate the relationship between magnetism and electricity. Each student group has a wooden block, paper clips, a battery, and some copper wire. What additional material is necessary to build a
simple motor?
A An iron nail is necessary to produce a temporary magnetic field.
B. A magnet is necessary to produce a permanent magnetic field.
C. An iron nail is necessary to act as the electrical circuit load.
D. A magnet is necessary to act as the electrical circuit load.

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.