Why do we see only one side of the moon from earth?
a. the moon does not rotate.
b. the moon takes longer to rotate than to revolve around earth.
c. the moon takes less time to rotate than to revolve around earth.
d. the moon’s period of rotation and revolution are equal.

What is the length x of the side of the triangle below? (hint: use the cosine function)

The movement of electrons between atoms is called an

Cyclotrons are widely used in nuclear medicine for producing short-lived radioactive isotopes. these cyclotrons typically accelerate h- (the hydride ion, which has one proton and two electrons) to an energy of 5 mev to 20 mev. this ion has a mass very close to that of a proton because the electron mass is negligible—about 1 2000 of the proton’s mass. a typical magnetic field in such cyclotrons is 1.9 t. (a) what is the speed of a 5.0-mev h-? (b) if the h- has energy 5.0 mev and b = 1.9 t, what is the radius of this ion’s circular orbit?