Answers TX-Physics CRFirst Law of Thermodynamics

First Law of Thermodynamics — Unit test Answers

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Sixty-three joules of heat are added to a closed system. The initial internal energy of the system is 58 J, and the final internal energy is 93 J.

28 J

30 J

88 J

151 J

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The diagram shows an engine piston before and after heat is added, which illustrates the laws of thermodynamics.

Substance X transfers thermal energy to substance Y through conduction. What is an accurate conclusion about the condition of both substances before conduction occurred?

Their molecules had the same amount of energy.

The substances were the same temperature.

Substance X’s molecules were faster than substance Y’s.

Substance X was cooler than substance Y.

Jin knows that the initial internal energy of a closed system is 78 J and the final internal energy is 180 J. He also knows that 64 J of energy are used to do work. To find the heat added to the system, Jin completes the steps below.1. Add the initial internal energy plus the final internal energy to find the change in internal energy. 2. Add the change in internal energy to the energy used to do work.3. Write the answer in joules.

For step 1, he should have used 180 J as the change in internal energy.

For step 1, he should have subtracted 78 J from 180 J to find the change in internal energy.

For step 2, he should have subtracted the change in internal energy from the energy used to do work.

For step 2, he should have subtracted the energy used to do work from the change in internal energy.

Which is the best example of decreasing entropy?

A box of nails is left in the rain and the nails rust over time.

A pile of dirt on a floor is cleaned up with a broom.

A puddle of water is exposed to the sun and evaporates.

A tree in a forest grows naturally over 10 years.

In the heat equation, what does Q represent?

heat required to raise the temperature

specific heat of the substance

mass of the substance

change in temperature

A heat engine has a temperature of 1800 K. Some of the heat from the engine flows to the surroundings, which are at a temperature of 160 K.

16%

91%

103%

109%

Chen explained that heat engines illustrate only the second law of thermodynamics because they involve the flow of thermal energy from hot to cool areas. His friend Mia disagreed and explained that these engines illustrate only the first law of thermodynamics because they are sometimes 100 percent efficient if they conserve enough energy.

Chen is incorrect because heat engines illustrate only the first law of thermodynamics.

Chen is incorrect because in heat engines thermal energy flows from cool to warm areas.

Mia is incorrect because heat engines illustrate only the second law of thermodynamics.

Mia is incorrect because machines and engines can never be 100 percent efficient.

According to the first law of thermodynamics, what could happen when heat is added to a system?

The internal energy of the system decreases.

The heat is turned into work done by the system.

New energy is created within the system.

Some of the energy in the system is destroyed.

The chart shows the temperatures of four different substances.

A substance has a specific heat of 0.870 J/g°C. It requires 2,000.0 joules to increase the temperature of 10.0 grams of the substance from its original temperature to its final temperature.

87.0°C

174°C

230°C

1,740°C

Suppose the exhaust system on a heat engine is not functioning properly. Which statement best explains how this will affect the engine?

The temperature of the gas will not increase during the compression stage.

Burned gases will not be released into the surrounding air.

The fuel-air mixture will not be able to enter the cylinder.

Combustion and subsequent gas expansion will not occur.

Which best describes the relationship between internal energy and thermal energy?

Thermal energy is a measure of the internal energy of a substance.

Internal energy is a measure of the thermal energy of a substance.

Internal energy is the portion of thermal energy that can be transferred.

Thermal energy is the portion of internal energy that can be transferred.

Allen made a diagram to compare radiation and conduction.

Must involve temperature differences between substances or objects

Occurs when molecules are in direct contact

Involves the movement of fluids based on density differences

Can occur where there is little or no matter

Temperatures of four liquid substances are shown in the chart.

Substance X will transfer thermal energy to substance Y mainly through radiation if they are mixed.

Substance Y will transfer thermal energy to substance Z through conduction if they are mixed.

Substance X will transfer thermal energy to substance W through radiation if they are placed near each other.

Substance W will transfer thermal energy to substance X through conduction if they are mixed.

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First Law of Thermodynamics — Unit test Answers

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