8TH GRADE PRACTICE
Physics Problems: Heat engines, Grade 8
Gas operation, engine design and efficiency.
Here the conditions and analysis of the solution can be read without an account. In the simulator, you need to collect the same analyzes yourself: “Given,” formulas, order of steps and answer.
Problem statements
The answer options are there to check against, and the walkthrough opens under each problem.
Problem #22
Gas operation and engine designEvaluate the statement: Gas does mechanical work when it expands and moves the piston or turbine blades.
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Some of the internal energy of the gas is converted into mechanical energy, and compression by an external force can increase the internal energy.
Answer
Problem #23
Gas operation and engine designEvaluate the statement: The concept “Internal combustion engine” means: A heat engine in which a flow of steam rotates a shaft, acting on a system of blades.
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The four-stroke cycle includes intake, compression, power stroke and exhaust; useful work is obtained mainly during the working stroke.
Answer
Problem #24
Heat enginesDuring which stroke of a four-stroke engine do heated gases directly perform useful work on the piston?
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Answer
Problem #25
Heat engine efficiency and environmentEvaluate the statement: A device that cyclically receives heat from a heater, performs work, and transfers some of the energy to the refrigerator.
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It is impossible to convert all the heat received into work, so the efficiency of any real heat engine is less than one.
Answer
Problem #26
Heat engine efficiency and environmentEvaluate the statement: the concept of “heat engine efficiency” means: The operation of heat engines is associated with the consumption of resources, heating of the environment and emissions of combustion products.
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Increasing efficiency reduces fuel consumption and the amount of excess heat for the same useful work.
Answer
Problem #27
Heat enginesThe engine received 400 kJ from the fuel and performed 120 kJ of useful work. Find the efficiency.
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Answer
The theory behind these problems
Work through the topic if a problem will not give in.
Formulas by topic
Look up symbols and units of measurement in the reference.