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 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum Jan 14th 2009, 03:21 PM #1 Junior Member   Join Date: Jan 2009 Posts: 1 Multiple Choice Questions on Fluids/Thermodynamics/Gases Hello all, I am doing my homework right now and I need some help with some questions on my homework that I did not understand It's multiple choice if that helps at all. If you could help show an explanation of how to get the correct answers or what formulas i should utilize. ANY help is greatly appreciated! Here they are 1) The Pressure inside a commercial airliner is maintained at 1 atm(10^5 Pa). What is the net outward force exerted on a 1m x 2m cabin door if outside pressure is equal to .30 atm? a)140, b) 1,400, c) 14,000 d) 140,000 ------------------- 2)By what factor is the total pressure greater at a depth of 850m in water than at the surface where pressure is one atmosphere? (water density=1 x 10^3 kg/m^3, 1 atmosphereic pressure = 1.01 x 10%5 N/m^2, and g=9.8) a)100, b)83, c)74, d)19 ------------------------ 3) Water is being sprayed from the nozzle of hose diameter 2 cm. The nozzle has an opening of .50 cm, and water leaves the hose at a speed of 10 m/s. What is the speed of the water in the hose? a).63 m/s, b).80 m/s, c)2.5 m/s, d) 10 m/s -------------------- 4)A cube of wood with a density of .78 g/cm^3 is 10cm on a side. When placed in water, what height will the cube float above the surface of the water? a)7.8 cm, b) 5 cm, c)2.2 cm, d)6.4cm -------------- 5)The pressure of 20g of an ideal monatomic gas is tripled while the volume is halved. What happens tot he internal energy? a)It stays the same b) Increases c) Decreases d)Indeterminate --------- 6) A solar heating system has 25% conversion efficiency. Solar radiation incident on solar panels is 1000 w/n^2. What is the increase in temperature of 30kg in a 1 hr period by a 4.0 m^2 area collector? a) 14.2 C b) 22.4 C, c)28.7 C d) 44.3 C ------- 7) Area on a p-v diagram has units associated with a) energy, b) momentum c) temperature d) change in temp ----- 8) A system acted on by surroundings receives 50J of heat while doing 20J of work. What is the net change of internal energy? a) 70 b) 30 c) 0 d) -30   Jan 14th 2009, 10:45 PM   #2
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 Originally Posted by jinger 1) The Pressure inside a commercial airliner is maintained at 1 atm(10^5 Pa). What is the net outward force exerted on a 1m x 2m cabin door if outside pressure is equal to .30 atm? a)140, b) 1,400, c) 14,000 d) 140,000
In this problem, you should know that Pressure = force/area
Then in this case, the net outward force should be
The difference in pressure times the area of door
 ------------------- 2)By what factor is the total pressure greater at a depth of 850m in water than at the surface where pressure is one atmosphere? (water density=1 x 10^3 kg/m^3, 1 atmosphereic pressure = 1.01 x 10%5 N/m^2, and g=9.8) a)100, b)83, c)74, d)19
Pressure= density X gravity X height below water
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 3) Water is being sprayed from the nozzle of hose diameter 2 cm. The nozzle has an opening of .50 cm, and water leaves the hose at a speed of 10 m/s. What is the speed of the water in the hose? a).63 m/s, b).80 m/s, c)2.5 m/s, d) 10 m/s
Cross-sectional area X speed= Cross-sectional area X speed
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 4)A cube of wood with a density of .78 g/cm^3 is 10cm on a side. When placed in water, what height will the cube float above the surface of the water? a)7.8 cm, b) 5 cm, c)2.2 cm, d)6.4cm
Something related to archimede's principle. A floating body must displace its own weight in which it floats. I guess you can find the mass and hence the weight of cube. Then find volume needed in water.
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 5)The pressure of 20g of an ideal monatomic gas is tripled while the volume is halved. What happens to the internal energy? a)It stays the same b) Increases c) Decreases d)Indeterminate
Internal energy = $\displaystyle \frac{3PV}{2}$

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 6) A solar heating system has 25% conversion efficiency. Solar radiation incident on solar panels is 1000 w/n^2. What is the increase in temperature of 30kg in a 1 hr period by a 4.0 m^2 area collector? a) 14.2 C b) 22.4 C, c)28.7 C d) 44.3 C
Is the solar radiation W/m^2?
If yes, find the actual power on heating by 1000X0.25
Then multiply this by the area you would get the power.
Power X time = Energy
Energy=mass X specific heat capacity X change in temperature
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 7) Area on a p-v diagram has units associated with a) energy, b) momentum c) temperature d) change in temp
It should be energy. You can just analyse the dimension of pV.
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 8) A system acted on by surroundings receives 50J of heat while doing 20J of work. What is the net change of internal energy? a) 70 b) 30 c) 0 d) -30
Heat = Change in internal energy + Work done  Tags choice, multiple, questions ,
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# by what factor is the total pressure greater at a depth of 850

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