Given capacitance & energy dissipated, find the charge Q

[courteous]

Homework Statement

A capacitance of 2\mu F having a charge Q_0 is switched into a series circuit of 10\Omega resistance. Find Q_0 if the total energy dissipated in the resistance is 3.60 mJ.

Ans. 120 \mu C

Homework Equations

Q=CV

The Attempt at a Solution

E=\int_0^\infty p(t)dt=\int_0^\infty \frac{v(t)^2}{R}dt=3.60 mJ

I need to extract V and use it in the equation for charge Q, right? Well, I don't know how.

 

[courteous]

I know that \overline{P}_{dissipated}\times t=\overline{P}_{supplied}\times t=3.60\text{ }mJ. How do I find V?

 

[Dmytry]

the energy stored in charged capacitor is v² * c / 2 .
You can find that formula if you note that V=Q/C and dE=V*dQ , and integrate charge from Q=0 to Q=Q₀ (you don't have to integrate by time, you can integrate by charge. Which makes more sense. Suppose I connected it to variable resistor that is being turned left and right by a monkey, the energy would of been the same, time doesn't matter there)

 

[courteous]

Thank you Dmytry!