A proton (mass 1.67 X 10^ -27 kg, charge= 1.6 X10 ^ -19 micro C) moves from point A to point B under the influence of an electrostatic force only. At point A the proton moves with a speed of 60 km/s. At point B the speed of the proton is 80 km/s. Determine the potential difference Vb-Va.