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# MCAS Heat problems

## 2015 MCAS Physics Exam

#4. The graph below shows how the temperature of a sample of water changes as energy is added to the sample.

During which interval does a gas form?
A. Q to R
B. R to S
C. S to T
D. T to U

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#21. Sunlight warms an area of Earth’s surface. Winds then carry thermal energy from this area to another location. Which two heat transfer processes are primarily involved in this situation?

C. conduction and convection
D. conduction and evaporation

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#24. Frozen food is submerged in a small insulated container of 95°C water. Which statement best describes the temperature of the food after two hours, assuming no heat is lost outside of the insulated container?

A. The temperature of the food will be 95°C.
B. The temperature of the food will be 100°C.
C. The temperature of the food will be the same as the temperature of the water.
D. The temperature of the food will be greater than the temperature of the water.

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#31 A student heats 200 g of water from 20°C to 70°C. How much heat did the student add to the water if the specific heat for water is 4.2 J/g C •° ?

A. 10,000 J            B. 14,000 J

C. 42,000 J            D. 76,000 J

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#44 A student was investigating cooling times for two pots made of different materials. One pot was stainless steel and the other pot was iron. The pots were placed on a table in a 25°C room. The pots were roughly the same size and shape, and contained the same amount of water. The pots and water were originally at 100°C. The student recorded the temperature of the water in each pot over time. The graph below shows the results.

a. Determine the amount of time it took the water in the iron pot to cool from 100°C to 60°C.

b. Based on the graph, which pot, the iron pot or the stainless steel pot, was a better conductor of thermal energy? Explain your answer.

c. Identify two methods of heat transfer that occurred as the water in the pots cooled, and describe how the transfer of heat occurred for each method.

d. Describe when the pots no longer experienced a net loss of thermal energy.

## 2016 MCAS Physics Exam

A 1 kg sample of liquid water and a 1 kg sample of ice are placed on a table. Which of the following statements best compares these two samples?

A. The liquid water has a larger volume than the ice.
B. The liquid water has a greater weight than the ice.
C. The liquid water has more thermal energy than the ice.
D. The liquid water has more gravitational potential energy than the ice.

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6. Two U.S. quarters, initially at the same temperature, are heated with a flame. One of the quarters was made before 1965 and is composed of silver. The
other quarter was made after 1965 and is composed mostly of copper.
What information is needed to determine which quarter will heat up faster?

A. the specific heats of the metals and the mass of each coin
B. the initial temperature of the coins and the mass of each coin
C. the temperature of the flame and the specific heats of the metals
D. the initial temperature of the coins and the temperature of the flame

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16. A fan enables a computer’s processor to run for long periods of time without overheating. Which of the following forms of heat energy transfer does this
example best represent?

A. condensation
B. convection
C. evaporation

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18. A small steel rod is placed in 5 L of water. The initial temperature of the steel rod is 120°C, and the initial temperature of the water is 10°C. When does heat stop flowing between the steel rod and the water?

A. when the steel rod reaches 65°C
B. when the water reaches its boiling point
C. when the steel rod reaches 10°C and the water reaches 120°C
D. when the steel rod and the water reach the same temperature

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27. Two identical objects, one hot and one cold, are placed near each other in a closed system. Which of the following graphs shows what happens to the temperatures of the objects over time?

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44. During cold periods, many orange growers repeatedly spray their trees with water to prevent the oranges from freezing. If the air is cold enough, the sprayed water freezes around the oranges, leaving the oranges themselves unfrozen.

a. Identify a measurement tool that orange growers use to measure the average kinetic energy of the air.
b. Describe what happens to the average molecular kinetic energy of the sprayed water
as it cools before it freezes.
c. Describe what happens to the average molecular kinetic energy of the sprayed water
as it freezes.
d. Explain how the phase change of the sprayed water may protect the oranges from freezing.

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### Sample “Open Response” answers: Question 44: Open-Response

Question 44: Open-Response
Reporting Category: Heat and Heat Transfer
Standard: 3.1 – Explain how heat energy is transferred by convection, conduction, and radiation.

A student was investigating cooling times for two pots made of different materials. One pot was stainless steel and the other pot was iron. The pots were placed on a table in a 25°C room. The pots were roughly the same size and shape, and contained the same amount of water. The pots and water were originally at 100°C. The student recorded the temperature of the water in each pot over time. The graph below shows the results.

a. Determine the amount of time it took the water in the iron pot to cool from 100°C to 60°C.

b. Based on the graph, which pot, the iron pot or the stainless steel pot, was a better conductor of thermal energy? Explain your answer.

c. Identify two methods of heat transfer that occurred as the water in the pots cooled, and describe how the transfer of heat occurred for each method.

d. Describe when the pots no longer experienced a net loss of thermal energy.

### Scoring Guide and Sample Student WorkSelect a score point in the table below to view the sample student response.

Score Description
4 The response demonstrates a thorough understanding of heat transfer by convection, conduction, and radiation and of thermal equilibrium.
The response correctly determines the time it took for water in the iron pot to cool to 60°C, and clearly explains which pot is a better conductor.
The response also correctly identifies and clearly describes two methods of heat transfer that occurred as the water cooled, and describes when the pots no longer experienced a net loss of thermal energy.
4
3 The response demonstrates a general understanding of heat transfer by convection, conduction, and radiation and of thermal equilibrium.
2 The response demonstrates a limited understanding of heat transfer by convection, conduction, and radiation and of thermal equilibrium.
1 The response demonstrates a minimal understanding of heat transfer by convection, conduction, and radiation and of thermal equilibrium.
0 The response is incorrect or contains some correct work that is irrelevant to the skill or concept being measured.

Note: There are 2 sample student responses for Score Point 4.