In an electrically heated home, the temperature of the ground in contact with a concrete basement wall is 13.6 oC. The temperature at the inside surface of the wall is 21.5 oC. The wall is 0.16 m thick and has an area of 7.3 m2. Assume that one kilowatt hour of electrical energy costs $0.10. How many hours are required for one dollar's worth of energy to be conducted through the wall?
So I know the formula for conduction is Q = (kA delta T)t/L, but I end up with two unknowns, Q and t. I feel like I'm almost there but I just can't make the final leap :/

Question

In an electrically heated home, the temperature of the ground in contact with a concrete basement wall is 13.6 oC. The temperature at the inside surface of the wall is 21.5 oC. The wall is 0.16 m thick and has an area of 7.3 m2. Assume that one kilowatt hour of electrical energy costs $0.10. How many hours are required for one dollar's worth of energy to be conducted through the wall?
So I know the formula for conduction is Q = (kA delta T)t/L, but I end up with two unknowns, Q and t. I feel like I'm almost there but I just can't make the final leap :/

anonymous · Answer

Q is not unknown ! 
You are given that you have to use 1 dollar worth of energy.
0.1 dollar provide 1 kilowatt hour heat
1 dollar will provide 10 kilowatt hour heat. (this is Q )
Insert the unknowns into the equation and find t
Use energy in joules not in kilowatt hour
1 kWh = 3.6 * 10^6 joules

anonymous · Answer

@Diwakar  Thank you so much! I understand now!