minibuttons
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I've got a few answers to some questions that I'd like to get checked if that's ok Please do correct me if I'm wrong by giving me hints to the right answer rather than just giving me the answer. I've also got some questions that I'm stuck on so please do give hints.

1.
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A piston is pressed into and open cylinder in the image show above.
Data: Density of air = 1.2 kgm^-3
Atmospheric pressure = 101kPa

1a) Calculate the force needed to reduce the volume in the cylinder if there is no change in temperature.
my answer: I got 5050 N by doing Force = Pressure * Area
1b) Calculate the force needed to reduce the volume in the cylinder if the temperature rises from 17 degrees C to 37 degrees C.
my answer: 5398 N
1c) How many moles of air are there in the piston?
my answer: not sure how to approach this. I know that the number of molecules is constant regardless of the increase of temperature but I'm just stuck on what to do...

2. Explain how the motion of molecules of a gas gives rise to pressure and how this can lead to a definition of absolute zero, 0 K.
my answer: I know that pressure and temperature are directly proportion so one increase with the other. Decrease in pressure causes the temperature to reduce because the motion of the molecules have been slowed down? - am I going down the right lane here with this?

3. A bubble rises from the bottom of a lake at 4 degrees C, to the top at 16 degrees C. The bubble doubles in volume when it reaches the top. Find the the pressure at the bottom of the lake:
Data: Atmospheric pressure = 101 kPa Density of water = 1000 kgm^-3
my answer: I have no idea where to begin but I have a feeling that I need to use some of the data above to calculate this...

Thank you for your time
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minibuttons
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bump~!
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Pennyarcade
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3) do you know the relationship between pressure volume and temperature?

Edit: just noticed 2, the relationship above should help you with it^
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minibuttons
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(Original post by Pennyarcade)
3) do you know the relationship between pressure volume and temperature?

Edit: just noticed 2, the relationship above should help you with it^
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Thank you, but for 2) am I saying the right things? I need to know whether I'm missing something from it.
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0le
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With part two, I'd always state the assumptions first. You should never state "Pressure is directly proportional to temperature" because in physics there will always be something weird that could be doing something else. I'm not an expert in this, but I'm assuming you are basing this on the Ideal Gas Law, so it might be best to have an opening statement saying "Given the assumptions used to derive the Ideal gas law..."

Regarding the actual answer, I'd say that due to the random motion of molecules in a gas, they can collide with the inner walls of the container which stores the gas. These collisions can occur more frequently with increases in temperature, or less frequently with decreases in temperature, both of which for a fixed volume.
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