A cyclist applies the brakes on her bicycle with a force of -75.0 N. As a result, the bicycle comes to rest after traveling 11.0 m with the brakes applied. How
much work is done by the brakes?
A. -75.0 N
B. 825 J
C. -825 J
D. 6.82 N. m


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?