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## Homework Statement

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?

## Homework Equations

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?

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