# Electric Potential slowing a charged particle to a stop

1. Mar 17, 2019 at 7:09 AM

### fight_club_alum

1. The problem statement, all variables and given/known data
A particle (mass 6.7 × 10–27 kg, charge 3.2 × 10–19 μC) moves along the positive x axis with
a speed of 4.8 × 105 m/s. It enters a region of uniform electric field parallel to its motion
and comes to rest after moving 2.0 m into the field. What is the magnitude of the electric
field?
a) 2.5 KN/C
b) 1.5 KN/C
c) 1.2 KN/C
d) 3.5 KN/C
e) 2.4 KN/C

2. Relevant equations
(delta)E.E = -q * (E.d)

3. The attempt at a solution
(1/2*(6.7*10^-27)*(4.8*10^5)^2)/( (3.2*10^-19) * 10^-6) *2)

The problem is that when I convert the charge from uc to c I get the answer but multiplied by a number like million and when I divide it by 1000 to get KN still the number remains multiplied by a factor of 1/10. On the other hand, if I leave the charge in uc I get the answer when I divide by 1000 as I should. I feel that I messed a step in the middle or there is a mistake in the question

Last edited by a moderator: Mar 18, 2019 at 9:54 AM
2. Mar 17, 2019 at 7:27 AM

### ehild

The smallest mass a particle (electron or proton) can have is 1.6 *10-19C. An ionized particle can have a multiple of it. So the μC should be a mistake.

3. Mar 17, 2019 at 8:34 AM

### fight_club_alum

yes, it turned out that the question is written incorrectly; (uc) should be (c) in this question.
Thank you so much

4. Mar 17, 2019 at 9:40 PM

### Miles123K

Think about the kinematic equations. What's the acceleration? Then use $F=ma$

5. Mar 17, 2019 at 11:00 PM

### haruspex

That was not the issue. See posts 2 and 3.