PHYSICS SAMPLE REVIEW QUESTIONS ANSWERS!!!
CHAP 10,11 (HEAT)
How much warmer should you get by eating a jelly doughnut?
A jelly doughnut gives about 250 Cal or 1046750 Joules. = Mass *C *ΔT
1, 046, 750 = 80kg *3470 J/kg°C * ΔT
ΔT = 3.77 °C warmer
What’s the difference between heat and temperature?
Heat is the change in energy, transfer of energy due to the movement of molecules, temperature is the average kinetic energy.
What is the end result of the second law of thermodynamics if the universe is one connected system?
Thermal equilibrium, thus same temperature (~4°K) everywhere, no work would be able to be done.
How high would a 3000 kg ice cube have to fall from for all of its energy to make it melt?
GPE = mgh =ΔQ=mHf, 3000 (9.8) h = 3000 * 335,000 = 1,005.000,000 Joules
H= 34, 183 meters
What is specific heat?
The amount of heat energy it takes to change 1 kg of a substance 1°C.
What is the difference in heat energy between solids, liquids, gases?
Gases have more… loose bonds, solids, tight bonds
What phase changes are cooling processes and why?
Liq to gas (evap) and Solid to Liq (freezing) take in heat to break bonds.
Why do you need more water and longer time to cook spaghetti in Denver?
Less air pressure, easier to boil, lower temperature, need more time to get heat to cook food.
Why does air cool down as it escapes from a diver’s compressed air tank?
Adiabatic cooling (expands rapidly NOT exchanging heat with surroundings, getting the energy to do work from the internal energy)
Why does a cup of hot water cooling never quite reach room temperature?
Hot water loses heat, room must gain some heat, so the final room temperature is higher than at the start.
What does the rate of something cooling depend on? Why?
How far away from the outside temp it is, the bigger the heat difference, the faster the rate of cooling.
Describe at the microscopic level why energy transfer by heat moves from an object at high temperature to an object at low temperature.
It has to do with the collisions between molecules, they even out in speeds, thus even out in heat.
How do you calculate the final temperature of coffee mixed with milk?
mCΔT=mcΔT, or MasscoffeeCcoffee(Ticoffee-Tf) = MassmilkCmilk(Tf-Timilk)
Tf =( McoffeeCcoffeeTicoffee + MmilkCmilkTimilk) / (MmilkCmilk + McoffeeCcoffee)
How much energy is required to evaporate 10 grams of water?
ΔQ = mHv = .010 (2,260,000) = 22,600 Joules
Describe the relationship between pressure, work and volume in a gas.
Work = Pressure* ΔVΔ
A balloon expanding quickly cools, while a balloon expanding slowly does not... Why?
When it expands quickly, it gets the energy from its internal energy, thus its temperature goes down. (Adiabatic cooling)
When it expands slowly, it gets the energy from the surroundings.
Why is the specific heat of water so high?
Because the bonds are very strong, water is a polar molecule.,