a helium nucleus (charge =2e, mass = 6.63E-27 kg) traveling at a speed of 6.20E5 m/s enters an electric field, traveling from point A, at a potential of 1.5E3 V, to point B, at 4.0E3 V. what is the speed at point B?
charge = 2e = 2 * 1.6E-19 C
delta V is potential difference.
i used equation delta V = - (delta KE)/q and derived the relationship:
delta V = - mass/2q (vf^2 - vi^2)
The Attempt at a Solution
since the charge is 2e and e for electron is -1.6E-19 C, so the right hand side is positive. the left side is 4.0E3-1.5E3...finally i solved vf and got 7.91E5 m/s but the answer is 3.78E5 m/s
i dont get it...where is the mistake?