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Physics Pressure

Hi,

Can you please help me to understand how to do this question? The answer is 48 balloons.
(edited 4 months ago)
Reply 1
You want to use the fact that the temperature doesn't change. So for an ideal gas, p1v1=p2v2.
Use this to find the volume of helium that you can fill up the balloons with, and then use the volume of helium in one balloon to work out how many you can have.

An important thing to keep in mind is when emptying the cannister of helium, the pressure won't reduce to 0 rather 1atm( roughly 1.1*10^5 pa).
Reply 2
I'm still not getting 48. Please tell me where I went wrong.

P1V1 = P2V2
(2.75 X 10^6) X (6 X 10^-3) = (1.1 X 10^5) X V2
V2 = 0.15 m3

0.15/ (3 x 10^-3) = 50 balloons


(edited 4 months ago)
Reply 3
Original post by S0303
I'm still not getting 48. Please tell me where I went wrong.

P1V1 = P2V2
(2.75 X 10^6) X (6 X 10^-3) = (1.1 X 10^5) X V2
V2 = 0.15 m3

0.15/ (3 x 10^-3) = 50 balloons



You're assuming the pressure in the cannister will be 0 after filling up the balloons. This is wrong, you will stop filling balloons once the pressure inside the cannister is equal to the pressure outside which is 1atm.
So instead of P1= 2.75*10^6 you should use P1= 2.64*10^6 to account for this.
Reply 4
Original post by Skiwi
You're assuming the pressure in the cannister will be 0 after filling up the balloons. This is wrong, you will stop filling balloons once the pressure inside the cannister is equal to the pressure outside which is 1atm.
So instead of P1= 2.75*10^6 you should use P1= 2.64*10^6 to account for this.

Ahh I see.. thank you so much! :smile:

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