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

a) What charge would need to be placed on a metal sphere such that the electric field produced stored a total of 50 J if the radius of the sphere was 18 cm?

b) How much work would need to be done to reduce the radius to 9 cm, assuming the sphere is (mechanically) easily compressible?

**2. Relevant equations**

V=(4/3)pi r^{2}

**3. The attempt at a solution**

Not sure where to tackle this problem…

http://ift.tt/OjgAc9