# Shuttle-ball experiment

1. Mar 22, 2013

### superconduct

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

2. Relevant equations

3. The attempt at a solution

By the inverse proportionality relation between electric potential energy and distance, why is the graph composed of straight lines only but not concave upwards slopes? My sketch and the solution are attached below.

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• ###### solution.jpg
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Last edited by a moderator: Mar 22, 2013
2. Mar 22, 2013

### TSny

When you say "inverse proportionality" between U and distance, are you thinking of U = kq1q2/r? That formula is for the potential energy of two point charges. But the problem deals with a point charge between parallel plates.

3. Mar 22, 2013

### superconduct

yeah I was thinking of that.
So the relation when in parallel plates is linear? Why??

4. Mar 22, 2013

### TSny

Can you describe the properties of the electric field between the plates?

5. Mar 22, 2013

### superconduct

the electric field is nearly uniform and varies linearly across the plates?

6. Mar 22, 2013

### TSny

E is (nearly) uniform, which means that it essentially doesn't vary at all as you move from one plate to the other. So, what can you conclude about the force acting on the ball as it moves between the plates?

7. Mar 22, 2013

### superconduct

The force is constant and work done varies linearly with distance?

8. Mar 22, 2013

### TSny

Yes, that's right.

9. Mar 22, 2013

### superconduct

thanks a lot for clearing my concepts :)