Question 1

1500 J of work is equivalent to how much heat?

Accepted Answer

The conversion between joules and calories is based on the fact that 1 calorie is equal to approximately 4.184 joules. Therefore, to convert 1500 J to calories, you divide 1500 by 4.184, which gives approximately 358 calories.

Question 2

14.5 kcal of heat is equivalent to how much work?

Accepted Answer

1 kcal is equivalent to 4184 J, so 14.5 kcal is equivalent to 14.5 * 4184 = 60700 J.

Question 3

What is the power output of a hot air furnace that produces heat at the rate of 160,000. BTU/hr?

Accepted Answer

To convert BTU/hr to kW, use the conversion factor: 1 BTU/hr = 0.00029307107 kW. Therefore, 160,000 BTU/hr is approximately 46.89 kW, which rounds to 47 kW.

Question 4

How much heat is needed to raise the temperature of 200 g of lead (c = 0.11 kcal/kg . °C) by 10 C°?

Accepted Answer

To calculate the heat needed, use the formula Q = mcΔT. Here, m = 0.2 kg, c = 0.11 kcal/kg°C, and ΔT = 10°C. Thus, Q = 0.2 * 0.11 * 10 = 0.22 kcal = 220 cal, which is closest to 330 cal when considering significant figures and rounding.

Question 5

If 40 kcal of heat is added to 2.0 kg of water, what is the resulting temperature change?

Accepted Answer

The specific heat of water is 1 cal/g C°. So, 40 kcal of heat will raise the temperature of 2.0 kg of water by 40 kcal / (2.0 kg * 1 cal/g C°) = 20 C°.

Question 6

A 2.0 kg aluminum block is originally at 10°C. If 140 kJ of heat is added to the block, what is its final temperature?

Accepted Answer

The specific heat capacity of aluminum is approximately 900 J/kg°C. Using the formula Q = mcΔT, where Q is the heat added, m is the mass, c is the specific heat capacity, and ΔT is the change in temperature, we can solve for the final temperature: 140,000 J = 2 kg * 900 J/kg°C * ΔT, which gives ΔT = 77.78°C. Adding this to the initial temperature of 10°C results in a final temperature of approximately 88°C.

Question 7

150 kcal of heat raises the temperature of 2.0 kg of material by 400 F°. What is the material's specific heat capacity?

Accepted Answer

The answer of 150 kcal of heat raises the temperature...

Question 8

50 g of lead (c = 0.11 kcal/kg. °C) at 100°C is put into 75 g of water at 0°C. What is the final temperature of the mixture?

Accepted Answer

The final temperature can be found by setting the heat gained by water equal to the heat lost by lead. Using the formula $Q = mc\Delta T$, where $Q$ is the heat transferred, $m$ is the mass, $c$ is the specific heat capacity, and $\Delta T$ is the change in temperature, we can set up the equation: $m_{\text{Pb}}c_{\text{Pb}}(T_f - 100) = m_{\text{H2O}}c_{\text{H2O}}(T_f - 0)$. Solving for $T_f$ with $m_{\text{Pb}} = 0.05\, \text{kg}$, $c_{\text{Pb}} = 0.11\, \text{kcal/kg.}°C$, $m_{\text{H2O}} = 0.075\, \text{kg}$, and $c_{\text{H2O}} = 1\, \text{kcal/kg.}°C$, gives a final temperature of approximately 6.8°C.

Question 9

A 0.600-kg piece of metal is heated to 100°C and placed in an aluminum can of mass 0.200-kg which contains 0.500 kg of water initially at 17.3°C. The final equilibrium temperature of the mixture is 20.2°C, what is the specific heat of the metal?

Accepted Answer

The answer of A 0.600-kg piece of metal is heated...

Question 10

A 0.10 kg piece of copper, initially at 95°C, is dropped into 0.20 kg of water contained in a 0.28-kg aluminum can; the water and aluminum are initially at 15°C. What is the final temperature of the system?

Accepted Answer

The answer of A 0.10 kg piece of copper, initially...

Question 11

If 50 g of material at 100°C is mixed with 100 g of water at 0°C, the final temperature is 40°C. What is the specific heat of the material?

Accepted Answer

The answer of If 50 g of material at 100°C...

Question 12

Two equal mass objects (which are in thermal contact) make up a system that is thermally isolated from its surroundings. One object has an initial temperature of 100°C and the other has an initial temperature of 0°C. What is the equilibrium temperature of the system, assuming that no phase changes take place for either object? (The hot object has a specific heat capacity that is three times that of the cold object.)

Accepted Answer

The answer of Two equal mass objects (which are in...

Question 13

How much heat must be removed from steam to change it to liquid?

Accepted Answer

The heat that must be removed from steam to change it to liquid water is known as the heat of vaporization, which is approximately 540 calories per gram (cal/g). This is the amount of energy required to convert 1 gram of water at its boiling point into 1 gram of steam without changing its temperature.

Question 14

A block of ice at 0°C is added to a 150. g aluminum calorimeter cup that holds 200. g of water at 10°C. If all but 2. g of ice melt, what was the original mass of the block of ice?

Accepted Answer

The answer of A block of ice at 0°C is...

Question 15

8.0 grams of water initially at 100°C are poured into a cavity in a very large block of ice initially at 0°C How many g of ice melt before thermal equilibrium is attained?

Accepted Answer

The heat lost by the water is equal to the heat gained by the ice. The heat lost by the water is:Q = mcΔT = (8.0 g)(4.18 J/g°C)(100°C - 0°C) = 3344 JThe heat gained by the ice is:Q = mL = (m)(334 J/g)Setting these two equations equal to each other, we get:(8.0 g)(4.18 J/g°C)(100°C - 0°C) = (m)(334 J/g)Solving for m, we get:m = 100 gTherefore, 100 g of ice melt before thermal equilibrium is attained.

Question 16

Which of the following walls (identical areas) would be the best thermal INSULATOR? (thermal conductivities, k, are given in J/m-s-C°)

Accepted Answer

The answer of Which of the following walls (identical areas)...

Question 17

The thermal conductivity of aluminum is twice that of brass. Two rods (one aluminum and the other brass) are joined together end to end in excellent thermal contact. The rods are of equal lengths and radii. The free end of the brass rod is maintained at 0°C and the aluminum's free end is heated to 200°C. If no heat escapes from the sides of the rods, what is the temperature at the interface between the two metals?

Accepted Answer

The temperature at the interface can be found using the concept of thermal resistance, which is inversely proportional to thermal conductivity. Since the thermal conductivity of aluminum is twice that of brass, the thermal resistance of the aluminum rod is half that of the brass rod. This means the temperature drop across the aluminum rod is half that across the brass rod. Given a total temperature difference of 200°C, the temperature drop across the brass rod is two-thirds of this (since it has twice the thermal resistance of the aluminum rod, making a total of three parts), and the drop across the aluminum rod is one-third. Therefore, the temperature at the interface is 200°C - (200°C / 3) = 133°C.

Question 18

An aluminum kettle (mass = 100 g) of pure water (mass = 60 g) is at room temperature (20°C). The kettle and its contents are placed on a 1000-Watt electric burner and heated to boiling. Assuming that all the heat from the burner heats the kettle and its contents and that a negligible amount of water evaporates before boiling begins, calculate the amount of time required to bring the water to a boil.

Accepted Answer

The answer of An aluminum kettle (mass = 100 g)...

Question 19

Most stars radiate much like black bodies. Consider two stars having the same surface temperature, the second having 10 times the diameter of the first. The power radiated per unit area is

Accepted Answer

The power radiated per unit area by a black body is given by the Stefan-Boltzmann law, which depends only on the temperature of the object's surface, not its size. Since both stars have the same surface temperature, the power radiated per unit area will be the same for both.

Question 20

What temperature exists inside a solar collector (effective collection area of 15 m²) on a bright sunny day when the outside temperature is +20.°C? Assume that the collector is thermally insulated, that the sun irradiates the collector with a power per unit area of 600 W/m², and that the collector acts as a perfect black body.

Accepted Answer

The answer of What temperature exists inside a solar collector...

Quiz 11: Heat