# Finding the change of internal energy

#### Ester

In moving out of a dormitory at the end of the semester, a student does 2.69 x 104 J of work. In the process, his internal energy decreases by 5.52 x 104 J. Determine each of the following quantities (including the algebraic sign): (a)W, (b) delta U, and (c)Q.

I get the following using formula: delta U = Q - W

(a) 2.69E4 J

(b) -5.52E4 J

(c) -28300 J

I know that part a and c are right, but part b isn't for some reason I do not understand. I think it should be right, but it marks it wrong. It's probably the easiest problem I've ever encountered, but for some reason I'm having trouble getting it. Does anyone know what the answer should be?

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#### abercrombiems02

perhaps the change in potential energy is his initial potential energy minus the work he does. If I have 5 units of energy in me, and I mow the lawn using two, I have 3 units of energy left for the day....make sense?

#### Doc Al

Mentor
Ester said:
I know that part a and c are right, but part b isn't for some reason I do not understand.
I don't understand how b could be wrong either; after all, dU is given in the problem statement. It looks correct to me. (And if b is wrong, how could c be right, since c depends on a and b.)

#### EnumaElish

Homework Helper
If a and c are right and the formula is right then b is right.

If b is not right then either a is wrong, and/or c is wrong, and/or the formula is wrong.

#### Ester

for some reason, my other friends use the same formula and get the answers that are the same as mine, and they get marked right, but i get marked wrong. :(

#### EnumaElish

Homework Helper
I would go talk to the professor who taught the class and gave the exam. Ask a friend of yours to be with you and take both sets of answers when you go to see the prof.

What is Q, by the way?

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