Newton's third law of motion explains that forces come in pairs, action forces and reaction forces. If the action force is a person kicking a ball, what would be the reaction force? * A. The force of friction on the ball
B. The force of friction on the kicker
C. The force of the ball pushing on the kicker's foot
D. The force of gravity on the ball

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?