8.3 6th Edition: Work being positive and negative

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ChathuriGunasekera1D
Posts: 78
Joined: Fri Sep 28, 2018 12:17 am

8.3 6th Edition: Work being positive and negative

Postby ChathuriGunasekera1D » Mon Jan 28, 2019 10:20 am

Hi! Can someone explain what work being positive or negative means, and how you can tell based off of the action that is being performed? This is the problem:

8.3 Air in a bicycle pump is compressed by pushing in the handle. If the inner diameter of the pump is 3.0 cm and the pump is depressed 20. cm with a pressure of 2.00 atm, (a) how much work is done in the compression? (b) Is the work positive or negative with respect to the air in the pump? (c) What is the change in internal energy of the system?

I understand (a), the answer is 28J, but I'm having issues with (b) and (c). Thank you!

Jordan Lo 2A
Posts: 85
Joined: Fri Sep 28, 2018 12:25 am

Re: 8.3 6th Edition: Work being positive and negative

Postby Jordan Lo 2A » Mon Jan 28, 2019 10:39 am

b) work is positive because a force is being applied to it that causes it to change volume
c) change in internal energy is the sum of heat energy and work energy. Since there isn't a change in heat, the change in internal energy is solely the work done on the system

Jordan Lo 2A
Posts: 85
Joined: Fri Sep 28, 2018 12:25 am

Re: 8.3 6th Edition: Work being positive and negative

Postby Jordan Lo 2A » Mon Jan 28, 2019 10:41 am

Can someone explain why we use 101.325 J/L*atm to convert w into joules for 8.3, but not for w in 8.9?

Madeline Ho 1C
Posts: 37
Joined: Mon Apr 23, 2018 3:00 am

Re: 8.3 6th Edition: Work being positive and negative

Postby Madeline Ho 1C » Mon Jan 28, 2019 6:23 pm

I still used 101.325 J/L*atm for 8.9. And then you have to convert it into kJ to solve for the change in internal energy.


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