In a Rutherford scattering experiment, an ?-particle (charge = +2e) heads directly toward a silver nucleus (charge = +47 e). The ?-particle had a kinetic energy of 4.7 MeV when very far (r ) from the nucleus. Assuming the silver nucleus to be fixed in space, determine the distance of closest approach. (Hint: Use conservation of energy with PE = keq1q2/r.)