Let the velocity of the Uranium nucleus be V, We have MV = mv where m and v are the mass of and velocity of alpha particle respectively. Now 0.5mv^2 = 5.15*(10^6)*1.6*(10^-19) = 8.24*10^-13 or v = [sq rt[8.24/(0.5*1.6*1.67)]* 10^7 m/s or v = 2.48*10^7 m/s We have MV = mv or V = (m/M)*2.48*10^7 = [(4*2.48)/235]*10^7 m/s or V = 4.23*10^5 m/s