# Work electron problem

1. Oct 18, 2004

### strugglin-physics

How much work is required to stop an electron (m = 9.11×10-31 kg) which is moving with a speed of 1.86×106 m/s?

Ef-Ei=W
Kenetic E - Potential E = Work
I don't think there is any potential energy in this case...

I'm a bit stuck. Any suggestions?

2. Oct 18, 2004

### Staff: Mentor

Keep going. $W = \Delta {KE}$, so what's the kinetic energy of that electron?

3. Oct 18, 2004

### strugglin-physics

is the change in kenetic energy 1/2mv^2?

4. Oct 18, 2004

### Staff: Mentor

The initial KE of the electron is 1/2mv^2; the final is zero. So, yes, the change in KE is (minus) 1/2mv^2.

5. Oct 18, 2004

### strugglin-physics

Great thank you that was a whole lot easier than I made it out to be!