A capacitor that powers the flash in a camera is charged using 6.0 V battery. after that capacitor is charged, it is discharged through the flashbulb in just 1.0 microsec. with avg power output of 20 w. whats is the capacitance?

Answer 1

80 W * 10^-6 s is the total discharge energy. That look like 8*10^-5 Joules to me.

Set that equal to the charged capacitor's stored energy ((1/2) C V^2)
and solve for V. They tell you what V = 6.0 V before the discharge.