Conversions to joules?


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Tyra Nguyen 4H
Posts: 74
Joined: Fri Sep 28, 2018 12:25 am

Conversions to joules?

Postby Tyra Nguyen 4H » Fri Feb 08, 2019 6:39 pm

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 did this problem and got the correct answer (28J), but as I redid it, I am getting 2.8 x 10-4 atm.m3. How do I convert these units to units of energy? I couldn't find anything on the equations and constants sheet.

Porus_Karwa_2E
Posts: 72
Joined: Fri Sep 28, 2018 12:24 am

Re: Conversions to joules?

Postby Porus_Karwa_2E » Fri Feb 08, 2019 7:14 pm

m^3 is equal to about 1000 L so you'd need to do the conversion of that to give you atm x L. 101.325 atmXL is equal to 1 joule. I believe this conversion is somewhere on the formula sheet for 14B.

Adrian C 1D
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

Re: Conversions to joules?

Postby Adrian C 1D » Fri Feb 08, 2019 7:18 pm

I think you were supposed to change the units earlier in the calculation to avoid this problem. It would be much easier to change the area of the cylinder, -141.37 cm ^, to L by dividing by 1000 ( since 1000 cm^3 make 1 L). Then when you found the work, it would be in L x atm, which can be changed into J by multiplying it by 101.325 J/(L x atm). This will cancel out L x atm and give you J.

Karishma_1G
Posts: 67
Joined: Fri Sep 28, 2018 12:18 am

Re: Conversions to joules?

Postby Karishma_1G » Sat Feb 09, 2019 1:08 pm

There are two conversions you can use to get your answer in terms of energy (Joules). 1cm3 = 1L and 1 L x atm = 101.325 J. Hope this helps!

KHuang1L
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

Re: Conversions to joules?

Postby KHuang1L » Sun Feb 10, 2019 7:57 pm

The formula sheet has the unit conversion equation from L.atm to J. To convert cm^3 to L in your answer, the formula sheet also has the unit conversion equation from dm^3 to L.


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