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-   -   I need help with questions on using energy, thermal properties and fluids and density (http://www.physicsforums.com/showthread.php?t=465955)

amandamarie29 Jan23-11 02:05 AM

I need help with questions on using energy, thermal properties and fluids and density
 
Im working on test corrections that are due tomorrow, and I was out sick for around a month and a half or so. I have been trying to find these in our book, however, our book is pretty much a big hunk of annoying weight that should be used for a campfire. Anyway, Im looking for some help with these problems.. and if you do answer could you please briefly write a sentence or two explanation so i can try and understand? thank you for all of your help!! =D

and the answers that i said i had put are incorrect.. thats probably really obvious i just wanted to clarify that... =)

10. A tire of an automobile has a gauge pressure of 30 psi at the top of a mountain, and the air temperature inside the tire is 300K. The atmospheric pressure at the top of the mountain is 0.7 atm. The car is driven down to sea level, where the atmospheric pressure is 1.0 atm and the air inside the tire is heated to 350 K. At sea level, assuming no leaks, the gauge pressure of the tire will be:
A) lower.
B the same.
C) higher.


I put C, but thats wrong and Im not sure why.. i thought pressure increased when temperature increased?


11. A barge loaded with lumber and iron ore floats in a lock by a dam ( a closed pool of water like a big swimming pool). If some of the cargo is thrown overboard, the level of the water in the lock will
A) rise, provided it is lumber that is thrown overboard.
B) stay the same.
C) rise, provided it is iron ore that is thrown over board.
D) drop.
E) rise.


I put C here as well. I thought since the lumber would float and the iron ore would sink. so the water would rise when the iron ore sank.


20. A perfectly insulated system has work done by it at a rate of 13 W. At what rate is the internal energy of the system changing?
A) 0 W
B) -13 W
C) 13 W
D) 6.5 W


I put A because i was thinking along the lines of it being an isolated system.. and i had to take a guess because i ran out of time.


31. The Tonga Trench in the Pacific Ocean is 36,000 feet deep. Assuming that sea water has an average density of 1.04 g/cm^3, calculate the absolute pressure at the bottom of the trench in atmospheres.
A) 1.1 x 10^6 atm
B) 1.1 x 10^8 atm
C) 1.1 x 10^3 atm
D) 1.1 x 10^5 atm
E) 2.1 atm


i dont even know how to start this one..


32. How much would a lead brick 2.0 in x 2.0 in x 8.0 in weigh if placed in oil with density p=0.92 g/cm^3?
A) 5.5 kg
B) 0.34 kg
C) 0.48 kg
D) 6 kg


or this one...


39. What is the total translational kinetic energy in a classroom filled with nitrogen at 1.01 x 10^5 Pa and 20.7 degrees C? The dimensions of the classroom are 4.60 m x 5.20 m x 8.80 m.

nobody in my class knew how to do this one...


5. Which of the following is a TRUE statement?
A) It is impossible to transfer heat from a cooler to a hotter body.
B) The second law of thermodynamics is a consequence of the first law of thermodynamics.
C) It is possible for heat to flow spontaneously from a hot body to a cold one or from a cold one to a hot one, depending on whether or not the process is reversible or irreversible.
D) It is not possible to convert work entirely into heat.
E) All of these statements are false.


I put A because i thought heat flowed from hot to cold


17. The Bernoulli effect is responsible for the lift force on an airplane wing. Wings must therefore be designed so as to insure that
A) air molecules move more rapidly past the lower surface of the wing than past the upper surface.
B) air molecules will be deflected downward when they hit the wing.
C) air molecules move more rapidly past the upper surface of the wing than past the lower surface.
D) wings are thick enough to create a significant pressure difference between the top and bottom surfaces of the wings because of the different heights of these surfaces.
E) air molecules will be deflected upward when they hit the wing.


i put A here too.. i was thinking along the lines that more air had to move under the plane to keep it in the air

any help is appreciated.. i feel really stupid and helpless right now =/

supratim1 Jan23-11 08:57 PM

Re: I need help with questions on using energy, thermal properties and fluids and den
 
hey, all my replies were deleted...oh......

supratim1 Jan23-11 08:59 PM

Re: I need help with questions on using energy, thermal properties and fluids and den
 
no. 11 - B. use archimedes principle.

supratim1 Jan23-11 09:00 PM

Re: I need help with questions on using energy, thermal properties and fluids and den
 
39. use Maxwell-Boltzmann distribution.

supratim1 Jan23-11 09:01 PM

Re: I need help with questions on using energy, thermal properties and fluids and den
 
5. D. no engine is 100% efficient. option A is principle of refrigerator.

supratim1 Jan23-11 09:02 PM

Re: I need help with questions on using energy, thermal properties and fluids and den
 
17. C. pressure difference.


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