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### Question 4B.3

Posted: Fri Feb 07, 2020 9:08 pm
Hello,
I got the first part of this question right, but not the second, I was curious if someone could help me figure out what I'm missing. Thank you!

The internal energy of a system increased by 982 J when it was supplied with 492 J of energy as heat. (a) Was work done by or on the system? (b) How much work was done?

b) Since change in internal energy = q + w => 982 = 492J + w => w=490
The answer key said 900J. I am a bit lost. Any help would be super appreciated!

Thank you,
Prasanna

### Re: Question 4B.3

Posted: Fri Feb 07, 2020 9:14 pm
In the solution manual that I have, 490 J is the correct answer. It is written as 4.90*102 J, but it is still the correct answer.

### Re: Question 4B.3

Posted: Fri Feb 07, 2020 10:34 pm
Yea the answer cannot be 900J because that would not make sense. if the change in internal energy is a + 982 and the supplied energy energy is also a + 492 then the equation would be +982= +492+ w where if you do math the work would have to be +490. My book also showed this as the answer(solution Manuel) it would also be why the since work is positive, work was done "on" the system.

### Re: Question 4B.3

Posted: Sun Feb 09, 2020 11:36 pm
Thank you guys for your replies! I used the answer key at the back of the book (I don't have the solution manual) and it said 90 * 10^2 J...I think that the answer key in the book is wrong since the solution manual also says 490.

### Re: Question 4B.3

Posted: Tue Feb 11, 2020 10:55 am
I feel you, it seems like there are so many typos in the textbook I don't really trust the answer key that much.

### Re: Question 4B.3

Posted: Tue Feb 11, 2020 11:31 am
It was a type I also stressed over it but yea it seems you were right.