PHY 102 Ch. 7

Calculate the quantity of heat needed to melt a 180-g block of ice at 0∘C. The heat of fusion L^f for water is 80 cal/g. Heat of fusion : Q=mL^f

14,400 cal (180 g x 80 cal/g)

A block of ice at 0∘C is dropped from a height that causes it to completely melt upon impact. Assume that there is no air resistance and that all the energy goes into melting the ice. What is the height necessary for this to occur? (Hint: Equate the joules of gravitational potential energy to the product of the mass of ice and its heat of fusion (Lf = 335,000 J/kg)

34 km; The answer DOES NOT depend on mass.

Find what heat in calories (cal) is needed to melt 60 g of 0∘C ice. The heat of fusion Lf for water is 80 cal/g.

4,800 cal

Rank the boiling-water temperature from highest to lowest in these locations: (a) Death Valley, (b) Sea level, and (c) Denver, CO (the "mile-high city").

A B C

Which would burn the most? a. 100 g of steam at 100°C b. 100 g of water at 100°C c. both equal

a. 100 g of steam at 100°C

When evaporation occurs, the molecules left behind in the water _______. a. All of these answers are correct. b. are less energetic c. result in lowered temperature d. have decreased average speeds

a. All of these answers are correct.

Does a good insulator prevent heat from getting through it, or does it simply delay its passage? a. Insulation delays heat transfer. b. Insulation prevent heat from getting through it.

a. Insulation delays heat transfer.

Which undergoes a faster rate of cooling: a red-hot poker in a warm oven or a red-hot poker in a cold room? (Or do both cool at the same rate?) a. a red-hot poker in a cold room b. a red-hot poker in a warm oven c. do both cool at the same rate

a. a red-hot poker in a cold room

The gush of steam that issues from the escape valve of a pressure cooker is relatively cool a. above the opening where expansion is prominent. b. close to the opening. c. none of the above

a. above the opening where expansion is prominent.

When a solid is changed to a liquid phase, the solid a. absorbs energy. b. releases energy. c. neither releases nor absorbs energy.

a. absorbs energy.

If you were caught in freezing weather with only a candle for warmth, you would be warmer in a. an igloo. b. a wooden house. c. a tent.

a. an igloo.

Cold water will warm to room temperature faster in a a. black pot. b. silver pot. c. depends on size, not color.

a. black pot.

Hot water will cool to room temperature faster in a a. black pot. b. silver pot. c. depends on size, not color.

a. black pot.

The dew that forms on a cold soda can when taken from a refrigerator is due to a. condensation. b. evaporation. c. sublimation. d. none of the above

a. condensation.

Steam burns are much more damaging than boiling-water burns because steam a. contains more thermal energy. b. has a higher temperature. c. is hotter. d. is gaseous.

a. contains more thermal energy.

Coastal winds shift from night to day due to a. convection. b. radiation. c. all about equally. d. conduction.

a. convection.

Hot steam that issues from a pressure cooker expands and a. cools. b. increases in temperature. c. can cause severe burns. d. all of the above e. none of the above

a. cools.

If a volume of air is warmed, it expands. If a volume of air expands, it a. cools. b. warms. c. neither

a. cools.

The process of convection occurs in a. fluids. b. gases. c. liquids. d. solids. e. none of the above

a. fluids.

When a volume of air is compressed, its temperature a. increases. b. decreases. c. neither

a. increases.

Your toes feel warmer on a rug than on a tile floor because the rug a. is a better insulator than tile. b. has more thermal energy than tile. c. is usually warmer than tile. d. all of the above e. none of the above

a. is a better insulator than tile.

At the same temperature, which move with the greater speed in a gas? a. light molecules b. heavy molecules c. both have equal average speeds

a. light molecules

One of the main reasons people can walk barefoot on red-hot coals of wood without burning their feet has to do with a. low thermal conductivity of the coals. b. low temperature of the coals. c. mind over matter techniques.

a. low thermal conductivity of the coals.

When salt is introduced to water, the temperature at which freezing occurs is a. lowered. b. increased. c. quite unaffected. d. dependent on the shape of salt and ice crystals.

a. lowered.

To change 50 g of boiling water to steam requires a. more calories than is required to bring 50 g of ice at absolute zero to the boiling point. b. 540 calories. c. 500 calories d. 50 calories. e. none of the above

a. more calories than is required to bring 50 g of ice at absolute zero to the boiling point.

Suppose you want to save energy and you're going to leave your warm house for a half hour on a cold day. You should turn the thermostat a. off. b. to room temperature. c. up. d. down

a. off.

Sublimation is a change of phase from solid to gas without a. passing through the liquid phase. b. a change of temperature. c. a transfer of energy.

a. passing through the liquid phase.

A good reflector of radiation is a a. poor absorber of radiation. b. good emitter of radiation. c. good absorber of radiation. d. none of the above

a. poor absorber of radiation.

The Earth loses heat mainly by a. radiation. b. conduction. c. convection. d. none of the above

a. radiation.

When water changes to ice, water molecules a. release energy. b. lose the quality of wetness. c. absorb energy. d. retain their energy.

a. release energy.

When water changes to ice, energy is _______. a. released by the water b. changed to a different form c. absorbed by the water d. None of the answers is correct.

a. released by the water

When a gas changes phase to become a solid, energy is a. released. b. unchanged. c. absorbed

a. released.

When a gas is changed to a liquid phase, the gas a. releases energy. b. absorbs energy. c. neither

a. releases energy.

Keep decreasing the shaking of atoms in a liquid and it will a. solidify. b. melt. c. harden.

a. solidify.

Keep increasing the shaking of atoms in a solid and it will a. sublime. b. melt. c. harden

a. sublime.

A friend says that a can of beverage will cool faster in the coldest part of a refrigerator. Knowledge of Newton's law of cooling a. supports this statement. b. shows this statement is false. c. none of the above

a. supports this statement.

What happens to the temperature of air when it expands? a. temperature decreases b. temperature increases

a. temperature decreases

When snow forms in clouds, the surrounding air is a. warmed. b. cooled and warmed. c. cooled. d. none of the above

a. warmed.

Suppose you walk on red hot coals with bare feet. Providing bits of coal do not stick to your feet, it would be safer if your feet are a. wet. b. dry. c. either

a. wet.

Does Newton's law of cooling apply to warming as well as to cooling? a. yes b. no

a. yes

If the greenhouse effect on Earth were absent, Earth's average temperature would be about a. as it is now. b. -18°C. c. appreciably warmer.

b. -18°C.

If the composition of the upper atmosphere were changed to permit a greater amount of terrestrial radiation to escape, what effect would this have on Earth's climate? a. If more terrestrial radiation in the upper atmosphere escaped, Earth's climate does not change. b. If more terrestrial radiation in the upper atmosphere escaped, Earth's climate would be cooler. c. If more terrestrial radiation in the upper atmosphere escaped, Earth's climate would be warmer.

b. If more terrestrial radiation in the upper atmosphere escaped, Earth's climate would be cooler.

Objects that are good radiators generally a. reflect radiation relatively well. b. absorb radiation relatively well. c. both d. neither

b. absorb radiation relatively well.

When water changes to steam, energy is _______. a. released by the steam b. absorbed by the steam c. changed to a different form d. None of the answers is correct.

b. absorbed by the steam

When ice changes phase to become water, energy is a. released. b. absorbed. c. unchanged

b. absorbed.

If you want to cook eggs by boiling them while in the mountains, then compared with cooking at sea level you should a. use a hotter flame. b. boil the eggs for a longer time. c. boil the eggs for a shorter time. d. none of the above

b. boil the eggs for a longer time.

Which requires more energy? a. melting a gram of 0°C ice b. changing 1 gram of 100°C water to 100°C steam c. increasing the temperature of 1 gram of water from 0°C to 100°C d. all the same

b. changing 1 gram of 100°C water to 100°C steam

Consider a steaming aluminum soda-pop can that contains a small amount of boiling water. When it is quickly inverted into a bath of cooler water, the can is dramatically crushed. This is due to the rapidly reduced pressure inside the can by a. rapid conduction of heat to the relatively cool water. b. condensation of steam inside. c. reduced thermal energy. d. contact with the relatively cool water. e. sudden slowing of the air and steam molecules inside.

b. condensation of steam inside.

Newton's law of cooling applies to objects that _______. a. cool b. cool or warm up c. warm up d. None of these answers is correct.

b. cool or warm up

The process of thermal convection mainly involves _______. a. radiant energy b. fluids c. insulators d. all of these answers

b. fluids

A poor conductor of heat is a a. poor insulator. b. good insulator. c. neither

b. good insulator.

The Sun's radiant energy is composed of shorter wavelengths than the Earth's because the Sun a. is an energy source while the Earth is primarily an energy receiver. b. has a higher temperature than the Earth. c. has much more thermal energy. d. none of the above

b. has a higher temperature than the Earth.

The higher the temperature of an object, the a. lower frequency it radiates. b. higher frequency it radiates. c. none of the above

b. higher frequency it radiates.

Food is cooked faster in a pressure cooker because of the a.increased thermal energy in the water. b. higher temperature. c. greater rate of bubble formation in the water. d. none of the above

b. higher temperature.

Glass and the atmosphere are largely opaque to a. visible light. b. infrared light. c. ultraviolet light.

b. infrared light.

A mixture of light and heavy molecules make up a sample of gas. The temperature of the gas is constant, which means all the molecules have the same average a. speed. b. kinetic energy. c. both d. none of the above

b. kinetic energy.

Suppose you want to save energy and you're going to leave your cool house for a half hour on a hot day. You should turn the temperature setting on the air conditioner a. up. b. off. c. down. d. to room temperature.

b. off.

A good heat conductor is a a. good insulator. b. poor insulator. c. neither

b. poor insulator.

Increased air pressure on the surface of hot water tends to a. promote boiling. b. prevent boiling. c. neither

b. prevent boiling.

Heat comes from the Sun to Earth by the process of _______. a. conduction b. radiation c. convection d. all of these, though radiation is greater

b. radiation

The silver coating on the glass surfaces of a Thermos bottle reduces energy that is transferred by a. conduction. b. radiation. c. friction. d. convection. e. none of the above

b. radiation.

An researcher discovers a harmless and tasteless salt, which, when added to water changes its boiling point. The market value for this salt will be best if the salt a. lowers the boiling point of water. b. raises the boiling point of water. c. either

b. raises the boiling point of water.

When gases change to a liquid phase, they a. absorb energy. b. release energy. c. neither absorb nor release energy.

b. release energy.

When steam condenses to water, energy is a. conserved as the phase change occurs. b. released. c. transformed to a different form. d. absorbed

b. released.

The wavelengths radiated by a high-temperature source are relatively _______. a. long b. short c. low in frequency d. None of these answers is correct.

b. short

The higher the temperature of an object, the a. longer the wavelengths it radiates. b. shorter the wavelengths it radiates. c. none of the above

b. shorter the wavelengths it radiates.

To minimize heat loss it is best that a teapot be a. black. b. silver. c. depends on size, not color.

b. silver.

To say you can never change only one thing means that when you change something, a. you can't do it again. b. something else changes. c. only one other thing will change.

b. something else changes.

The interior of a greenhouse emits long-wavelength radiation due to its a. green color. b. temperature. c. plant cell structure. d. transparency

b. temperature.

Which emits the highest frequency of radiation? a. a blue-hot star b. the Sun c. a red-hot star d. all the same

b. the Sun

A can of soft drink will cool faster if placed in what part of a refrigerator? a. the main part of the refrigerator b. the freezer compartment c. both locations should cool the can at the same rate

b. the freezer compartment

A water-filled paper cup held in a flame will not catch fire because a. paper is a good conductor of heat. b. the paper cup cannot become appreciably hotter than the water it contains. c. the inside of the paper is wet. d. water is an excellent conductor of heat.

b. the paper cup cannot become appreciably hotter than the water it contains.

Which is not a phase of matter? a. gases b. vacuum c. liquids d. solids

b. vacuum

The molecules in a room-temperature glass of water jostle around at a. much the same speeds. b. constant speeds. c. a great variety of speeds.

c. a great variety of speeds.

In the mountains, water boils at a. a higher temperature than at sea level. b. the same temperature as at sea level. c. a lower temperature than at sea level.

c. a lower temperature than at sea level.

Heating the Earth's atmosphere is caused by energy a. production. b. consumption. c. both d. neither

c. both

If an object radiates more energy than it absorbs, its a. thermal energy decreases. b. temperature decreases. c. both d. neither

c. both

If an object radiates more energy than it reflects, its a. temperature decreases. b. thermal energy decreases. c. both d. neither

c. both

Put a saucer of water on your table. A process that occurs in the saucer is a. evaporation. b. condensation. c. both d. neither

c. both

Warm air rises because faster moving molecules tend to move to regions of less a. density. b. pressure. c. both

c. both

In a gaseous mixture of hydrogen and oxygen, the higher-temperature molecules are a. hydrogen. b. oxygen. c. both the same d. not enough information

c. both the same

If air were a better conductor than it is, nighttimes on Earth would be a. not appreciably different in temperature. b. considerably warmer. c. considerably colder.

c. considerably colder.

Compared to a glass of ice water with ice, a glass of plain ice-cold water without ice on a warm day will warm up a. in the same amount of time. b. slower. c. faster

c. faster

When bringing water to a boil in the mountains, the time needed to reach the boiling point is a. more than at sea level. b. the same as at sea level. c. less than at sea level.

c. less than at sea level.

Food in boiling water cooks slower in high-altitude locations. If you increase the temperature under the pot the food will cook a. slower. b. faster. c. neither

c. neither

Melting and freezing are _______. a. mysterious to the physics community b. one and the same process c. opposite processes

c. opposite processes

If molecules in a sample of gas moved so they completely missed each other, the gas's temperature would a. increase. b. decrease. c. remain unchanged.

c. remain unchanged.

Suppose you are served coffee at a restaurant before you are ready to drink it. In order for it to be the hottest when you are ready for it, you should add cream a. when you are ready to drink the coffee. b. at any time. c. right away.

c. right away.

Convection currents in the air near a seashore are produced by a. varying temperatures. b. shifting winds. c. unequal heating of land and water. d. none of the above

c. unequal heating of land and water.

The process of boiling water tends to

cool the water

The number of grams of ice that can be melted by 1 g of 100°C steam is a. 0.125 g. b. 6.75 g. c. 0.148 g. d. 8 g. e. none of the above

d. 8 g.

A star that is twice as hot as another has twice the a. kelvin temperature. b. any of the above c. Celsius temperature. d. Fahrenheit temperature. e. none of the above

d. Fahrenheit temperature.

Melting and freezing are both a. processes of molecular transfer. b. opposite processes. c. changes of phase. d. all of the above

d. all of the above

Radiant energy emitted by our planet is a. terrestrial energy. b. electromagnetic. c . the result of radioactivity in Earth's interior. d. all of the above

d. all of the above

The process of boiling that occurs in water tends to _______. a. have no effect on the water's temperature b. warm the water c. both warm and cool the water at the same time d. cool the water

d. cool the water

Boiling and freezing can occur at the same time when water is subjected to a. increased atmospheric pressure. b. decreased temperatures. c. increased temperatures. d. decreased atmospheric pressure.

d. decreased atmospheric pressure.

A substance absorbs heat energy by the process of a. convection. b. radiation. c. conduction. d. none of the above

d. none of the above

To melt 50 g of 0°C ice requires a. 25 calories. b. 50 calories. c. 80 calories. d. none of the above

d. none of the above

Evaporation is a cooling process because a. of conduction and convection. b. heat is radiated during the process. c. the temperature of the remaining liquid decreases. d. the more energetic molecules are able to escape the liquid. e. none of the above

d. the more energetic molecules are able to escape the liquid.

What are the three common ways in which heat is transferred?

radiation, convection, conduction