# Point Charge help?

1. Jul 8, 2008

### waleye262

1. The problem statement, all variables and given/known data

A point charge of mass 0.069 kg and charge q = +5.89 µC is suspended by a thread between the vertical parallel plates of a parallel-plate capacitor.

If the angle of deflection is 22°, and the separation between the plates is 0.025 m, what is the potential difference between the plates?

2. Relevant equations

U = .5C*V^2

3. The attempt at a solution

I know the left has a higher potential energy because the mass is attracted toward the right?

2. Jul 8, 2008

### Hootenanny

Staff Emeritus
Welcome to PF,

If the charge is displaced to the right, then the left would indeed be at a higher potential.

Can you start by determining the tension in the string?

3. Jul 8, 2008

### waleye262

The tension of the string is m*g= .68

I am still lost at how to find the the force that attracts it to the side.

would it be 5.89E-6 cos 22?

4. Jul 8, 2008

### Hootenanny

Staff Emeritus
That would be correct if the string was hanging vertically, but that isn't the case is it?

5. Jul 8, 2008

### waleye262

no its not hanging vertically so mg=cos22???

I am sorta lost...

6. Jul 8, 2008

### Hootenanny

Staff Emeritus
You're getting closer:

$$T\cos22 = mg$$

Now since the mass is in equilibrium, what can you say about the horizontal forces acting on the mass?

7. Jul 8, 2008

### waleye262

alright so the force acting on the mass is the same as the tension force which is 0.729.

so would you use F=q(v/x)?

8. Jul 8, 2008

### Hootenanny

Staff Emeritus
Remember that you want the horizontal component of the force, not the vertical.