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Phy 242
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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University Physics Test 1 help:
1) A diatomic gas in a 6L container is originally at 21C and atm pressure. It is heated at constant volume until temp is 113C, then at constant pressure until the gas has increased its volume by 0.46L. How much thermal energy is required? Internal energy of gas change? Work done in the process?
2) A certain material has density 4.3kg/L. If 0.73 kg of the material are suspended from a string and immersed in a liquid whose density is 0.85kg/m^3, whats the tension in the string?
3) Air passes over the top of an airplane wing at 235m/s and over the bottom at 210m/s. If the wing has area 13m^2, how much lift results?
4) Water is descending in a vert pipe of d=7cm and open to the atmosphere. At a lower point, the water flows into a smaller pipe d=0.77cm. At a certain instant the depth of the water just above the narrowing point is 32cm and the water is moving at 198cm/s. How fast will the water be going as it exits a small hole just above the narrowing point?
5) Find an expression for the avg pressure exerted by N identical particles each of mass m traveling always at speed v on one end wall of a cylindrical container of length L meters and c.s. area Am^2, provided the particle travels always along the axis of the cylinder and collides elastically with the ends of the container. Use your expression to show whether the pressure is proportional/inversely to the N or proportional/inversely to N^2.
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1) First state (V=6L, T=21C should convert to K, P=Patm) Second state (V=6L, T=T1, P=Patm + __) Third state (V=6+0.46=6.46L, T=T2, P=Patm + __) I don't know how to use this info to then answer the 3 questions?!
@& Thermal energy change is
1/2 n R `dT per degree of freedom, and all this thermal energy goes into internal energy
2/2 n R `dT if expanding against constant pressure, none of which goes into internal energy.
The gas is diatomic so there are 3 translational and 2 rotational degrees of freedom.*@
2) Well I know that density = m/v, but I don't think I would use that simple method on this. If so, then there are two densities, which one do you use?!
@& The buoyant force is equal to the weight of fluid displaced and acts upward.
The gravitational force is equal to the weight of the object and acts downward.
The tension is whatever it needs to be to hold the system in equilibrium, with zero net force.*@
3) Air density is 0.00129 gm/cm^3, top v= 235m/s, bottom v=210m/s, and area is 13m^2. Is lift a certain method or equation?! Or is it just asking for displacement!? I just can't figure out what I'm trying to solve for.
@& Bernoulli's equation, and the density of air, will give you the pressure difference due to the different velocities. There is little difference in vertical distance y between top and bottom of wing, so rho g y is small.
Multiply that pressure difference by the wing area and you get the lift.*@
4) I think this one is similar to prob set 5 problem 7, not sure if its the same. Area for lg pipe (pi*(3.5^2)) sm pipe (pi*(0.385^2)). (3.5/0.385)^2 = 82.645?! 82.645 * 198 = 16363.7?! This is the only calculations I could come up with to get a start on this problem. Am I headed in the right direction or not?!
@& You are.
Now use Bernoulli's Equation to compare 1/2 rho v^2 and rho g y at the surface of the water, and at the exit point of the hole. The pressure is the same at both points, atmospheric pressure.*@
5) This is the problem that I am finding myself clueless about. Would this particular problem be like the one experiment we did in class with the BB and the tile?! I'm so lost on this one, and I'm sure it's probably not that hard...
@& Figure out the momentum change for each collision with a given wall, and the time between collisions.
Then apply the impulse-momentum theorem.
We've worked this out more than once in class, and it's also in the intro problem sets. However try working it out from my note without referencing those notes and problem sets. *@
@& See if my notes help. You're welcome to insert more work in some and/or all of these, and I'll be glad to review it.
Mark insertions with **** so I can separate them from the rest of the document.*@