# Help with physics gas laws question

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Thread starter 1 month ago
#1
A water fire extinguisher contains about 4 litres of air at 10^7 Pa and 20∘C. When the extinguisher is used, this gas forces the water out. Calculate the pressure when the volume has increased to 10 litres and the temperature has dropped to about 3.0 ∘C. Give your answer to 2 significant figures.
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1 month ago
#2
Use PV/T = constant
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1 month ago
#3
(Original post by Luwei)
Use PV/T = constant
To second this poster, make sure the temperatures are converted into Kelvin.
1
1 month ago
#4
(Original post by anonymous12345.)
A water fire extinguisher contains about 4 litres of air at 10^7 Pa and 20∘C. When the extinguisher is used, this gas forces the water out. Calculate the pressure when the volume has increased to 10 litres and the temperature has dropped to about 3.0 ∘C. Give your answer to 2 significant figures.
You need to use the combined law, as pressures, volumes and temperatures are given and they are constant. That is to say that the ratio of this law does not change, if you put the values for the quantities in the formula P1V1/T1 = P2V2/T2.

(Original post by Driving_Mad)
To second this poster, make sure the temperatures are converted into Kelvin.
So true, that has not to be forgotten
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