Q4M5 Pretest

What is the function of a heat engine?

• It converts chemical energy to mechanical energy.

• It converts thermal energy to mechanical energy.

• It converts mechanical energy to chemical energy.

• It converts thermal energy into chemical energy.

Among the methods by which heat may be converted into work,

which is the least practical?

• the bicycle

• burning gases

• the steam engine

• atomic reactor

What is the correct sequence of four cycle-stroke of gasoline engine?

1. Intake 2. Exhaust 3. Power 4. Compression

• 1,2,3,4

• 1,4,3,2

• 2,3,4,1

• 1, 3,4,2

Describe the piston and the gases during a power stroke.

• The piston moves down, the exhaust valve opens and the burned gas expelled out through the exhaust valve.

• The piston moves down. No heat enters or leaves the system.

• 1. The piston ignites the mixture. This will increase the temperature.

• 1. The piston moves up. Heat enters or leaves the system.

1. What is the process of compression and expansion of gas

2. so that no heat enters or leaves a system?

• Adiabatic

• Isothermic

• Sobaric

• Thermal expansion

Why is heat engine not 100% efficient?

• All mixture of gases is converted into work.

• Some of the gases is exhausted in the surroundings.

• All of the gases are used up by the engine.

• Some of the gases is taken up in the piston.

How work input/ temperature in the cold reservoir

is related to thermal efficiency?

• The lesser the work input/ temperature in the cold reservoir, the greater the efficiency of the heat engine.

• The lesser the work input/ temperature in the cold reservoir, the lesser the efficiency of the heat engine.

• The greater the work input/ temperature in the cold reservoir, the greater the efficiency of the heat engine.

• The lesser the efficiency of the heat engine, The lesser the work input/ temperature in the cold reservoir.

How work output/ temperature in the hot reservoir

is related to thermal efficiency?

• The greater the efficiency of the heat engine, the greater the work output in the hot reservoir.

• The lesser the work output in the hot reservoir, the lesser the efficiency of the heat engine.

• The greater the work output in the hot reservoir, the greater the efficiency of the heat engine.

• The greater the work output in the hot reservoir, the lesser the efficiency of the heat engine.

What is the efficiency of a gasoline engine that receives 172 J of energy

from combustion and loses 105 J by heat to exhaust during one cycle?

• 38.75%

• 38%

• 39%

• 39.75%

Suppose a steam engine receives steam at 500K. The engine uses part of this thermal energy for work. It exhausts the rest to a condenser at a temperature

of 300K. What is the maximum efficiency of this steam engine?

• 50%

• 60%

• 70%

• 80%