Question 1

In a liquid at a given temperature, the molecules are moving in every direction, some fast, some slowly. Electrical forces of adhesion tend to hold them together. However, occasionally one molecule gains enough energy (as a result of collisions) so that it pulls loose from its neighbors and escapes from the liquid. Which of the following can best be understood in terms of this phenomenon?

Accepted Answer

When you step out of a swimming pool and stand in the wind, the wind increases the rate at which water molecules gain enough energy to escape from the liquid (evaporation), which in turn draws heat away from your body more rapidly, making you feel colder. This process is a direct application of the described phenomenon of molecules escaping from a liquid.

Question 2

A chunk of ice (T = -20°C) is added to a thermally insulated container of cold water (T = 0°C). What happens in the container?

Accepted Answer

When a chunk of ice at -20°C is added to water at 0°C, heat flows from the warmer water to the colder ice. This heat transfer causes some of the water to freeze, adding to the mass of the ice, until thermal equilibrium is reached. The process continues until the temperatures equalize, with the system likely reaching a temperature below 0°C but not colder than -20°C, depending on the masses of ice and water involved.

Question 3

You blow on food to cool it. Blowing increases

Accepted Answer

Blowing on food increases the airflow around it, enhancing the convection process, which is the transfer of heat through the movement of fluids (in this case, air). This increased airflow helps carry away the heat from the food more efficiently, cooling it down.

Question 4

Which of the following would be the best radiator of thermal energy?

Accepted Answer

A perfectly black surface is the best radiator of thermal energy because it absorbs all wavelengths of light and also emits thermal radiation more efficiently than surfaces that reflect light, such as shiny, metallic, or white surfaces. Styrofoam is a poor conductor and radiator of heat.

Question 5

By what primary heat transfer mechanism does one end of an iron bar become hot when the other end is placed in a flame?

Accepted Answer

Conduction is the primary heat transfer mechanism in solids like an iron bar, where heat moves through the material from the hot end to the cooler end.

Question 6

A large fan placed in a closed room is effective by enhancing

Accepted Answer

A large fan enhances air circulation within a room, promoting the heat transfer process known as convection. Convection involves the movement of warmer air away from the heating source and cooler air towards it, facilitating temperature regulation.

Question 7

By what primary heat transfer mechanism does the sun warm the Earth?

Accepted Answer

The sun warms the Earth primarily through radiation, as electromagnetic waves travel through the vacuum of space to reach and heat the Earth's surface.

Question 8

In the vacuum of space, one gets rid of unwanted heat from spacecraft by utilizing

Accepted Answer

In the vacuum of space, convection and conduction are not effective because they require a medium (like air or a physical object) to transfer heat. Evaporation requires a liquid to turn into gas, which is not practical or efficient in the vacuum of space. Radiation, however, does not require a medium; it is the process by which heat is emitted as electromagnetic waves and can effectively be used to get rid of unwanted heat from spacecraft.

Question 9

A layer of insulating material with thermal conductivity K is placed on a layer of another material of thermal conductivity 2K. The layers have equal thickness. What is the effective thermal conductivity of the composite sheet?

Accepted Answer

The answer of A layer of insulating material with thermal...

Question 10

Consider two neighboring rectangular houses built from the same materials. One of the houses has twice the length, width, and height of the other. Under identical climatic conditions, what would be true about the rate that heat would have to be supplied to maintain the same inside temperature on a cold day? Compared to the small house, the larger house would need heat supplied at

Accepted Answer

The rate at which heat needs to be supplied is proportional to the surface area through which heat is lost. Doubling each dimension of the house doubles the length and width of each face, so each face has 4 times the area, and since there are 6 faces (4 walls, a roof, and a floor), the overall effect is that the larger house has 4 times the surface area of the smaller house. However, the total increase in surface area does not mean the heat needs to be supplied at 6 times the rate because the increase in volume (and thus space to heat) is by a factor of 8 (2x length * 2x width * 2x height), but the rate of heat supply depends on the surface area through which heat is lost, not the volume. Therefore, the correct answer is that the larger house would need heat supplied at 4 times the rate of the smaller house to maintain the same inside temperature.

Question 11

If you double the absolute temperature of an object, it will radiate energy

Accepted Answer

The rate at which an object radiates energy is proportional to the fourth power of its absolute temperature, according to the Stefan-Boltzmann law. Therefore, if the absolute temperature is doubled, the energy radiated will increase by $2^4 = 16$ times.

Question 12

Gasoline yields 4.8 × 10⁷ joules per kg when burned. The density of gasoline is approximately the same as that of water, and 1 gal = 3.8 L. How much energy does your car use on a trip of 100 mi if you get 25 mi per gallon?

Accepted Answer

The answer of Gasoline yields 4.8 × 10⁷ joules per...

Question 13

The water flowing over Niagara Falls drops a distance of 50. m. Assuming that all the gravitational energy is converted to thermal energy, by what temperature does the water rise?

Accepted Answer

The answer of The water flowing over Niagara Falls drops...

Question 14

0.45 kg of a metal at 90.° C is added to 0.40 kg of water at 20.0° C.
(a) If the final temperature of the mixture is 26.° C, what is the specific heat of the metal?
(b) specific heat determined in part "a"given the same data?

Accepted Answer

The answer of 0.45 kg of a metal at 90.°...

Question 15

A 100. gram steel bullet moves at 250. m/s just before imbedding itself into a thick anchored wood post. If 40.% of the initial kinetic energy goes into heating the bullet (steel c = 460.J/kg-C)
(a) how hot does the bullet become if it initially is at 25.°C?
(b) what would be the bullet's temperature if it had been twice as massive ( 2 times 100. grams)?

Accepted Answer

The answer of A 100. gram steel bullet moves at...

Question 16

How much heat would be required to melt 1.0 kg of LEAD, initially at room temperature? Assume room temperature to be 20° C. (c = 920 J/kg-C° _Lf = 0.25 × 10⁵ J/kg LV = 8.67 × 10⁵ J/kg melts at 328.°C boils at 1744.°C)

Accepted Answer

The answer of How much heat would be required to...

Question 17

The heat of fusion of ice is 80. kcal/kg-C°. When 50. g of ice at 0°C is added to 50. g of water at 25°C, what is the final temperature?

Accepted Answer

The answer of The heat of fusion of ice is...

Question 18

The heat of fusion of lead is 5.9 kcal/kg, the heat of vaporization is 207. cal/kg, and its melting point is 328°C. How much heat is required to melt 50. g of lead initially at 23°C? (The specific heat of lead is 0.031 kcal/kg-C°. )

Accepted Answer

The answer of The heat of fusion of lead is...

Question 19

Ice cream, when eaten, gives about 2100. Calories/kg to the body. On the other hand, the body must give back energy to warm it up to body temperature (37°C). Assuming ice cream has similar thermal properties to water:
(a) 1/2 kg produces how much energy?
(b) 1/2 kg absorbs how much energy to reach 37°C?
(c) What is the net gain or loss (eating 1/2 kg ice cream)?

Accepted Answer

The answer of Ice cream, when eaten, gives about 2100....

Question 20

Consider a light bulb, in empty space, radiating 200. watts with its filament heated to 2800.°C. Assuming it is a good approximation to a black body.
(a) What is the area of the filament?
(b) If placed in an oven, with walls at 800.°C, what is its net power radiated now?

Accepted Answer

The answer of Consider a light bulb, in empty space,...

Quiz 11: Heat

A chunk of ice (T = -20°C) is added to a thermally insulated container of cold water (T = 0°C) . What happens in the container?

You blow on food to cool it. Blowing increases

Which of the following would be the best radiator of thermal energy?

By what primary heat transfer mechanism does one end of an iron bar become hot when the other end is placed in a flame?

A large fan placed in a closed room is effective by enhancing

By what primary heat transfer mechanism does the sun warm the Earth?

In the vacuum of space, one gets rid of unwanted heat from spacecraft by utilizing

A layer of insulating material with thermal conductivity K is placed on a layer of another material of thermal conductivity 2K. The layers have equal thickness. What is the effective thermal conductivity of the composite sheet?

If you double the absolute temperature of an object, it will radiate energy

Gasoline yields 4.8 × 10⁷ joules per kg when burned. The density of gasoline is approximately the same as that of water, and 1 gal = 3.8 L. How much energy does your car use on a trip of 100 mi if you get 25 mi per gallon?

The water flowing over Niagara Falls drops a distance of 50. m. Assuming that all the gravitational energy is converted to thermal energy, by what temperature does the water rise?

0.45 kg of a metal at 90.° C is added to 0.40 kg of water at 20.0° C. (a) If the final temperature of the mixture is 26.° C, what is the specific heat of the metal? (b) specific heat determined in part "a"given the same data?

How much heat would be required to melt 1.0 kg of LEAD, initially at room temperature? Assume room temperature to be 20° C. (c = 920 J/kg-C° _Lf = 0.25 × 10⁵ J/kg LV = 8.67 × 10⁵ J/kg melts at 328.°C boils at 1744.°C)

The heat of fusion of ice is 80. kcal/kg-C°. When 50. g of ice at 0°C is added to 50. g of water at 25°C, what is the final temperature?

The heat of fusion of lead is 5.9 kcal/kg, the heat of vaporization is 207. cal/kg, and its melting point is 328°C. How much heat is required to melt 50. g of lead initially at 23°C? (The specific heat of lead is 0.031 kcal/kg-C°. )

Consider a light bulb, in empty space, radiating 200. watts with its filament heated to 2800.°C. Assuming it is a good approximation to a black body. (a) What is the area of the filament? (b) If placed in an oven, with walls at 800.°C, what is its net power radiated now?

Quiz 11: Heat

A chunk of ice (T = -20°C) is added to a thermally insulated container of cold water (T = 0°C) . What happens in the container?

You blow on food to cool it. Blowing increases

Which of the following would be the best radiator of thermal energy?

By what primary heat transfer mechanism does one end of an iron bar become hot when the other end is placed in a flame?

A large fan placed in a closed room is effective by enhancing

By what primary heat transfer mechanism does the sun warm the Earth?

In the vacuum of space, one gets rid of unwanted heat from spacecraft by utilizing

A layer of insulating material with thermal conductivity K is placed on a layer of another material of thermal conductivity 2K. The layers have equal thickness. What is the effective thermal conductivity of the composite sheet?

If you double the absolute temperature of an object, it will radiate energy

Gasoline yields 4.8 × 107 joules per kg when burned. The density of gasoline is approximately the same as that of water, and 1 gal = 3.8 L. How much energy does your car use on a trip of 100 mi if you get 25 mi per gallon?

The water flowing over Niagara Falls drops a distance of 50. m. Assuming that all the gravitational energy is converted to thermal energy, by what temperature does the water rise?

0.45 kg of a metal at 90.° C is added to 0.40 kg of water at 20.0° C. (a) If the final temperature of the mixture is 26.° C, what is the specific heat of the metal? (b) specific heat determined in part "a"given the same data?

How much heat would be required to melt 1.0 kg of LEAD, initially at room temperature? Assume room temperature to be 20° C. (c = 920 J/kg-C° Lf = 0.25 × 105 J/kg LV = 8.67 × 105 J/kg melts at 328.°C boils at 1744.°C)

The heat of fusion of ice is 80. kcal/kg-C°. When 50. g of ice at 0°C is added to 50. g of water at 25°C, what is the final temperature?

The heat of fusion of lead is 5.9 kcal/kg, the heat of vaporization is 207. cal/kg, and its melting point is 328°C. How much heat is required to melt 50. g of lead initially at 23°C? (The specific heat of lead is 0.031 kcal/kg-C°. )

Consider a light bulb, in empty space, radiating 200. watts with its filament heated to 2800.°C. Assuming it is a good approximation to a black body. (a) What is the area of the filament? (b) If placed in an oven, with walls at 800.°C, what is its net power radiated now?

Gasoline yields 4.8 × 10⁷ joules per kg when burned. The density of gasoline is approximately the same as that of water, and 1 gal = 3.8 L. How much energy does your car use on a trip of 100 mi if you get 25 mi per gallon?

How much heat would be required to melt 1.0 kg of LEAD, initially at room temperature? Assume room temperature to be 20° C. (c = 920 J/kg-C° _Lf = 0.25 × 10⁵ J/kg LV = 8.67 × 10⁵ J/kg melts at 328.°C boils at 1744.°C)