In a Rutherford scattering experiment, assume that an incident `alpha particle (radius 1.80fm) is moving directly toward a target gold nucleus (radius 6.23fm). If the alpha particle stops right at the surface of the gold nucleus, how much energy did it have to start with?

An alpha particle (the nudeus of a helium atom) (with charge +2) is accelerated and moves in a vacuum tube with kinetic energy 10 MeV. It passes through a uniform magnetic field of 1.88T, and traces a circular path of radius 24.6cm. Obtain the mass of the alpha particle. [leV = 1.6 xx 10^-19 J , charge of electron = 1.6 xx 10^-19C ]