# Speed of a charged object accelerated through a potential difference

## Homework Statement

A 5.0 g object carries a net charge of 3.8uC. It acquires a speed v when accelerated from rest through a potential difference V. A 2.0 g object acquires twice the speed under the same circumstances. What is its charge?

## The Attempt at a Solution

I don't really know where to start for this one. I know I need to find the force on the object to find the acceleration, then use uniform accelerated motion equations to find the velocity. But I'm not really sure how to begin using only the charge and potential difference. If I find the electric field, then I can find the force. So the first step I suppose is to find the electric field of this area with potential difference V. Any tips would be appreciated. Thanks!

use energ principle

qV = .5mv2

Is there another way to do this? Or can you explain where this equation comes from?

There is but its difficult for me to make you understand that method.
OK, lets try ...

Consider that the charge traveled some distance l while acquiring velocity v.

- write the electric field from one point of q to another.
- use that to find force
- use force to find acceleration of the particle.
- use newton's eqn of motion relating initial, final velocity , acc. and distance travelled

The only problem with that is that I have no points of reference for distances. I tried using delta V = delta U/q, but I don't know if that necessarily holds without reference points.

You dont need reference points.

Displacement remains same even if origin is shifted!!!