Question
Asked by:
$10.00 physics
- From Physics: General-Physics
- Closed, but you can still post tutorials
- Due on May. 18, 2009
- Asked on Apr 28, 2009 at 8:27:38PM
Q:1. You have a 12 oz cup of coffee at 180 degrees F. You add 2 ounces of cold water at 40 degrees F. What is the temperature of the coffee?
2. You take a 50 g glass coffee mug from the dishwasher following the dry cycle. You use a dishcloth because the temperature of the mug is 90 C. You fill the mug with 250 g of cold water from the refrigerator. The temperature of the water is 5 C. Assume no heat is lost to either the air, the kitchen counter, or to your hand (all stupid assumptions, but what the heck). What will be the final temperature of the cup, and of the water in it? [Specific heats: glass, 837 J/(kg)(C); water, 4186 J/(kg)(C) ]
3. An air bubble at the bottom of a lake has a volume of 15 cm3. The lake is 40 m deep and has a temperature of 4 C at the bottom. The bubble then rises to the surface where the temperature is 23 C. What is the volume of the bubble just before it reaches the surface? (Assume the surface of the lake is at sea level. Don't neglect atmospheric pressure!)
4. You are sitting behind a curtain watching meters that measure pressure, volume, and temperature of some kind of heat engine. Pressure, volume, and temperature have reached an equilibrium state. Then someone behind the curtain tells you that they are going to add energy to the system. The energy is added and the equilibrium changes. Can you tell whether they did work on the system, heated the system, or a combination of both? Explain your answer.
5. In a refrigerator, heat is transferred from a colder area (the inside of the refrigerator) to a warmer area (the air outside of the refrigerator). Given what you know about internal energy, explain how this is possible.
6. A spacecraft power system generates electricity by absorbing heat from a nuclear reactor operating at 500 C and expelling heat from a radiator operating at 100 C. What is the theoretical maximum efficiency of the system? (Don't forget, temperatures must be in K, not C!)
