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course Phy 202
Physics II Practice Test Problem Number 2
There is a small amount of water at the bottom of a sealed container of volume 7.6 liters which is otherwise full of an ideal gas. A thin tube open to the atmosphere extends down into the water, and up to a height of 143 cm. The system is initially at atmospheric pressure and temperature 141 Celsius.
• If we increase the temperature of the gas until water rises in the tube to a height of 99 cm, then what is the temperature at that instant?
Bernoulli's Equation will give us the new pressure.
If the tube is thin then volume change is negligible so PV = nRT tells us that P / T is constant.
From init pressure, final pressure, init temp we easily find final temp.
&&&& .5rhov+rhogH+P=.5rhov+rhogH+P
I then get stuck….Could you guide me with this problem?
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If the water in the tube is moving, it's not moving fast enough to make much difference, as the 1/2 rho v^2 term (and note that v is squared) will be much smaller than the change in rho g h (you can verify this; even if the water is moving at 1 m/s, 1/2 rho v^2 is much less than the change in the rho g h term for this problem).
Eliminating the 1/2 rho v^2 term you get
rho g h_1 + P_1 = rho g h_2 + P_2.
From this you can easily find the change in pressure, which would be P_2 - P_1.
This would allow you to calculate P_2, since you know P_1.
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I eventually need to do P1/T1=P2/T2 (in Kelvin)
Problem Number 5
The masses of 1 mole of various gases are as follows: hydrogen about 2 grams, helium about 4 grams, nitrogen about 28 grams, oxygen about 32 grams and carbon dioxide about 44 grams. On the average how fast does a molecule of each gas move at 333 Celsius?
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.5mv^2=3/2kT
I know to use this equation, but stuck on what to do….
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You can find the masses of the molecules. A mole contains an Avagadro's number of molecules.
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Check my notes and let me know if you have additional questions.
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