A proton travels through uniform magnetic and electric fields.The magnetic field is B = -2.50i mT. At one instant the velocity ofthe proton is v=2000j m/s. At that instant and in unit-vectornotation, what is the net force acting on the proton if theelectric field is
(a) 4.00kV/m
(b) -4.00k V/m and
(c) 4.00iV/m?