# Inflating balloon

#### S_fabris

This is one of many postings from me this week :yuck: unfortunately I'm just not getting the correct answers...anyway here I go :

A toy balloon is inflated with helium at a constant pressure that is 4.2e5 Pa in excess of atmospheric pressure. If the balloon inflates from a volume of 1.4e-4m3 to 9.6e-4m3, how much work is done by the balloon on the surrounding air? answer in J
this is my work

P= 4.2e5Pa + 101300Pa
= 521 300 Pa
dV = (Vf-Vi) = (9.6e-4 - 1.4e-4)
= 0.00082m3

W= 521 300Pa x (0.00082m3)
427.466 J (incorrect on homework server)

I'm guessing it has something to do with the work on the surrounding air...I have been looking in my books and course notes for this and I can't find anything...can anybody help me out??

Any help is appreciated,
Sergio

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#### Mindscrape

Is this what the problem is supposed to be: A toy balloon is inflated with helium at a constant pressure that is $$4.2e^5$$ Pa in excess of atmospheric pressure. If the balloon inflates from a volume of $$1.4e^{-4}m^3$$ to $$9.6e^{-4}m^3$$, how much work is done by the balloon on the surrounding air? answer in J

(?)

#### S_fabris

Yes thats exactly the question on my homework page :)

#### S_fabris

Hey we finally got the answer...for the pressure...do not add the atmospheric pressure...simply use the one in the question

Sergio

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