# Change in electric potential energy

1. Feb 13, 2010

### Physics197

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

A tire of radius 32.5 cm has a surface that is conducting. A charge of 4.89×10-8 C is then placed on the surface. The potential on the balloon's surface is 1.35E+03 V. Later, suppose that some of the air is let out of the tire, so that the radius shrinks to 10.5 cm, the new potential on the balloon's surface is 4.19E+03 V.

What is the change in electrical potential energy during the shrinking process?

2. Relevant equations

Change in electric potential energy = q (change in electric potential)

3. The attempt at a solution

$$\Delta$$U = q($$\Delta$$V) = (4.89e-8C)(4190J/C-1350J/C) = 1.4e-4 J

But that doesnt work.

2. Feb 13, 2010

### Physics197

anyone have a clue, or a hint

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