PH 202 Exam1 Practice Problems

PH 202 – Exam1 Practice Problems

Following is some sample problems to gauge your preparation for exam1. They are to show you what area you may need to reinforce and study more. (Note: your test may include problems that no sample is shown in this practice exam)

1. You buy an "airtight" bag of potato chips packaged at sea level, and take the chips on an airplane flight. When you take the potato chips out of your luggage, you notice it has noticeably "puffed up." Airplane cabins are typically pressurized at 0.75atm , and assuming the temperature inside an airplane is about the same as inside a potato chip processing plant, by what percentage has the bag "puffed up" in comparison to when it

was packaged? (Hint: find V/V1) Ans: 33%

2. Absolute zero is what temperature on the Fahrenheit scale? Ans: –459.67 oF

3. A scuba tank has a volume of 5000 cm3 . For very deep dives, the tank is filled with 50% (by volume) pure oxygen and 50% pure helium. How many molecules are there of each type in the tank if it is filled at 25 oC to a gauge pressure of 16 atm?

Ans: 1.74 mol of each

4. When a 290-g piece of iron at 180 oC is placed in a 95-g aluminum calorimeter cup containing 250g of glycerin at 10 oC , the final temperature is observed to be 38 oC . Estimate the specific heat of glycerin. Ans: 2300 J/kg oC

5. Will potatoes cook faster if the water is boiling more vigorously? Explain.

6. A gas is enclosed in a cylinder fitted with a light frictionless piston and maintained at atmospheric pressure. When 2300 kJ of heat is added to the gas, the volume is observed to increase slowly from 12.5 m3 to 15.4 m3.

A) Calculate the work done by the gas. Ans: 1560 kJ

B) Calculate the change in internal energy of the gas. Ans: 740 kJ 7. It is not necessary that a heat engine's hot environment be hotter than ambient temperature. Liquid nitrogen (77 K ) is about as cheap as bottled water. What would be the efficiency of an engine that made use of heat transferred from air at room temperature (293 K ) to the liquid nitrogen "fuel"? Ans: 74%

8. A 7-kg person has an apparent weight of 530 when standing in water that comes up to the hips. Estimate the mass of each leg. Ans: 11.5 kg

9. A horizontal pipe with a 50 cm2 right end cross sectional area gradually narrows to 12.5 cm2on the left end. When water flows through this pipe at a certain rate, the gauge pressure in these two sections is 31.0 kPa and 22.0 kPa, respectively. What is the volume rate of flow? Ans: 0.055m/s

10. You need to siphon water from a clogged sink. The sink has an area of 0.35 m2 and is filled to a height of 4.0 cm as shown. Your siphon tube rises 45 cm above the bottom of the sink and then descends 85 cm to a pail as shown in the figure. The siphon tube has a diameter of 3.0 cm. Assuming that the water level in the sink has almost zero velocity, estimate the water velocity when it enters the pail.

Ans: 2.9 m/s