If objects in free fall near the surface of Earth accelerate downward at 9.81 meters per second, why does a feather not accelerate at this rate when dropped near the surface of Earth? A. The feather's mass is too small. B. The air spaces in the feather interfere with gravity. C. Air friction acts on the feather. D. The shape of the feather propels it through the air.

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?