# Homework Help: Work and velocity

1. Oct 19, 2007

### Ry122

Problem: A proton moving at 6.5x10^6 m/s encounters an electric field of 4500 volt/meter.
How fall will the proton penetrate the field before stopping. (Electric field and proton are moving in opposite directions)

My attempt:
First I found the kinetic energy of the proton, then I found the force that the electric field exerted on the proton with F=Eq. The force would do the sane amount of work on the proton as the kinetic energy the proton had to make it stop so I used w=fs with w=kinetic energy and solved for s. The answer was 49m but the answer in the book is 10.49m.
Can someone tell me where I went wrong?

2. Oct 19, 2007

### learningphysics

Your idea is right... must have been your calculations that went wrong... can you show your steps?

3. Oct 19, 2007

### Ry122

Mass of proton = 1.67 x 10^-27
q of proton = 1.6 x 10^19
using ke = 1/2mv^2 kinetic energy = 3.527875 x 10^14
using F=Eq, F=7.2 x 10^16
W=f x s
W/F = S

4. Oct 19, 2007

### learningphysics

I'm also getting 49m. Double check to make sure you have the question right...