The basic definition or formula for this condition is 1 watt = 1 joule / second
The formula is W = J/T
W = watts
J = joules
T = Time = ???
Givens
W = 3 kW = 3000 W
J = 9 megaJoules = 9 * 10^6 Joules
T = time in seconds.
Solution
3000 = 9 * 10^6 / T Multiply both sides by T
3000*T = 9*10^6 Divide by 3000
T= 9*10^6 / 3000 = 3000 seconds which is 5/6 of an hour. Answer
