How many time constants must elapse in a capacitor?

[yogotah]

Homework Statement

How many time constants must elapse if an initially charged capacitor is to discharge 55% of its stored energy through a resistor?

Homework Equations

The Attempt at a Solution

I don't even know where to start, so please a nudge in the right direction would help.

Thanks!

 

[gneill]

Homework Statement

How many time constants must elapse if an initially charged capacitor is to discharge 55% of its stored energy through a resistor?

Homework Equations

The Attempt at a Solution

I don't even know where to start, so please a nudge in the right direction would help.

Thanks!

Well, what equations do you know that might be related to the problem? Clearly there's an RC circuit with the capacitor discharging from some initial value (charge or voltage, either will do). What's the expression that describes that? What's an expression for the energy stored in a capacitor?