Energy Question-(don't know which equation to use?)

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In summary, the conversation is about a question regarding the use of an equation to solve a problem involving the energy leakage in a house. The problem involves keeping the house at a certain temperature using electricity and calculating the average energy leakage in joules per second. After some discussion, the solution is found to be 12250 watts. There is also a mention of another problem with different numbers and a different solution, but it is unclear how the problem should be solved.
  • #1
quickclick330
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Energy Question--(don't know which equation to use?)

I don't know how to start the problem, any help or hints would be greatly appreciated.

I'm gussing you are supposed to use Ethermal = mCdT but not sure how to apply it to this question. Thanks again!:-)


During 4 hours one winter afternoon, when the outside temperature was 5° C, a house heated by electricity was kept at 23° C with the expenditure of 49 kwh (kilowatt·hours) of electric energy.

(a) What was the average energy leakage in joules per second (watts) through the walls of the house to the environment (the outside air and ground)?

(b)The rate at which energy is transferred between two systems due to a temperature difference is often proportional to their temperature difference. Assuming this to hold in this case, if the house temperature had been kept at 26° C (77° F), how many kwh of electricity would have been consumed?
 
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  • #2
Assuming all the electricity is converted to heat... how much energy leaves the house... remember the temperature is remaining constant at 23 degrees...

You have the energy... divide by time to get rate of energy leakage.
 
  • #3
i calculated energy to be 49kw/h = 49000 w/h = 49000 J / (4 hours X 60) = 204.1
is that right?
 
  • #4
quickclick330 said:
i calculated energy to be 49kw/h = 49000 w/h = 49000 J / (4 hours X 60) = 204.1
is that right?

No. you're given 49kwh. kwh is a unit of energy not power... kw*h not kw/h... you can convert kwh to joules if you want. But you don't need to...

Divide energy by time... ie divide 49kwh by the time...
 
  • #5
Solved! Thanks for the help :-)
 
  • #6
I have the exact same problem but I don't understand the energy principal just yet (hasn't clicked) I can't get the answer for part a
 
  • #7
I ran out of guesses/failed :( but I still need to learn how to do that for the test so anymore help would be appreciated
 
  • #8
solrac214 said:
I have the exact same problem but I don't understand the energy principal just yet (hasn't clicked) I can't get the answer for part a

The temperature is kept constant. The idea is that all of the 49kwh is converted to heat... but if that is the case all that heat must leave the house... reason being that the temperature in the house is constant... so heat entering house - heat leaving the house = 0.

So 49kwh is lost over 4 hours... so the rate at which energy is lost if 49kwh/4h = 12.25kw.
 
  • #9
tried that and it wasn't the right answer =(
 
  • #10
solrac214 said:
tried that and it wasn't the right answer =(

really? did you need to enter the answer in W or kW?

oh... the question asks for watts... so 12250W...
 
  • #11
my friend had the numbers 4 hrs 4 degrees outside 22 degrees inside and 51 kwh and his answer was 1417.17 watts if that helps but someone else solved it for him
 
  • #12
solrac214 said:
my friend had the numbers 4 hrs 4 degrees outside 22 degrees inside and 51 kwh and his answer was 1417.17 watts if that helps but someone else solved it for him

Hmmm... I'm curious how this problem should be solved then...
 

FAQ: Energy Question-(don't know which equation to use?)

1. What is the equation for calculating energy?

The equation for calculating energy is E = m * c^2, where E represents energy, m represents mass, and c represents the speed of light.

2. How do I know which equation to use for a specific energy question?

The equation to use for a specific energy question depends on the type of energy being considered. For example, if the question involves kinetic energy, you would use the equation E = 1/2 * m * v^2, where m represents mass and v represents velocity. If the question involves potential energy, you would use the equation E = m * g * h, where m represents mass, g represents the acceleration due to gravity, and h represents the height of the object.

3. Can I use the same equation for all types of energy?

No, different types of energy have different equations to calculate them. For example, thermal energy is calculated using the equation E = m * c * ΔT, where m represents mass, c represents specific heat capacity, and ΔT represents the change in temperature.

4. How do I convert energy from one form to another?

To convert energy from one form to another, you can use the equation E = Q + W, where E represents the total energy, Q represents heat, and W represents work. This equation takes into account the transfer of energy between different forms.

5. Is there a universal equation for all types of energy?

No, there is not a universal equation for all types of energy. Each type of energy has its own specific equation, and it is important to use the correct equation for the specific type of energy being considered.

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