# Displacement of a particle

1. Feb 13, 2016

### Melssssss

1. The problem statement, all variables and given/known data
A particle of charge +14.5http://edugen.wileyplus.com/edugen/courses/crs6407/art/qb/qu/c18/lower_mu.gifC and mass 5.09 × 10-5 kg is released from rest in a region where there is a constant electric field of +328 N/C. What is the displacement of the particle after a time of 4.40 × 10-2 s?

http://edugen.wileyplus.com/edugen/courses/crs6407/art/qb/qu/c18/w1706-chap18prob49.gif

2. Relevant equations
electric force= qE
Elecrtic force= ma

3. The attempt at a solution
I have found the force and the acceleration from above equations. hoe do I use that information to go further.

2. Feb 13, 2016

### TSny

Hint: Is the acceleration constant?

3. Feb 13, 2016

### Melssssss

4. Feb 13, 2016

### TSny

If you know the acceleration and the time, how do you get displacement? You would have studied this early in your coverage of mechanics.

5. Feb 13, 2016

### Melssssss

but the velocity is changing, the picture of it wouldn't load.

6. Feb 13, 2016

### TSny

Yes, the velocity is changing.

Suppose a particle starts at rest and moves with constant acceleration, a, for a time, t. Can you express the final velocity, vf, in terms of a and t? If you can do that, then you can use the result for vf to help get the displacement.

7. Feb 15, 2016

### Melssssss

ta + v(initial)

8. Feb 15, 2016

### TSny

OK. For this problem the initial velocity is 0. So, the final velocity is vf = at. What would be the average velocity during the time t?

9. Feb 15, 2016

### Melssssss

in this case, 4.1128.
so then I would plug all this into this equation
x= vf2-vo2/2a?

10. Feb 15, 2016

### TSny

On the formatting toolbar there is an icon for superscripts. So, your equation is x= (vf2-vo2)/(2a). Note the parentheses that I added to make the equation correct according to the rules of "order of operations".

This is one of the well-known formulas for constant acceleration that I was referring to in post #4. This equation will get to the answer if you first calculate vf.

However, if you are familiar with those constant acceleration equations, there is one that would be more convenient for this problem. Do you know of a formula that relates x, vo, a, and t?

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