Mechanical Aptitude Test Mechanical Aptitude Heat Transfer and Thermodynamics Questions and Answers 2 — Questions and Answers
Question 1: The First Law of Thermodynamics is best described as:
- Heat always flows from cold to hot
- Energy cannot be created or destroyed, only converted (Correct answer)
- Entropy of a closed system always increases
- Work equals force times distance
Correct answer: Energy cannot be created or destroyed, only converted
The First Law is the conservation of energy: energy changes form but the total amount in a closed system remains constant.
Question 2: In a heat engine, after performing useful work, waste heat is exhausted into:
- The hot reservoir
- The cold reservoir (Correct answer)
- The working fluid
- The crankshaft
Correct answer: The cold reservoir
A heat engine absorbs heat from a hot reservoir, converts some to mechanical work, and must expel the remainder into a cold reservoir.
Question 3: A pressure cooker cooks food faster because increased pressure inside the vessel:
- Lowers the boiling point of water
- Raises the boiling point of water above 100°C (Correct answer)
- Directly increases heat from the burner
- Circulates steam more rapidly
Correct answer: Raises the boiling point of water above 100°C
Higher pressure raises water's boiling point above 100°C, allowing food to cook at higher temperatures and therefore faster.
Question 4: Thermal expansion in metals means that when temperature increases, the metal will:
- Contract and become denser
- Expand as atomic vibrations increase spacing (Correct answer)
- Become harder and more brittle
- Only change length, not volume
Correct answer: Expand as atomic vibrations increase spacing
Increased thermal energy causes metal atoms to vibrate with greater amplitude, increasing the average spacing between atoms and causing overall expansion.
Question 5: The Carnot efficiency of a heat engine depends on:
- The specific working fluid used
- Only the absolute temperatures of the hot and cold reservoirs (Correct answer)
- The physical size of the engine
- The operating pressure of the fluid
Correct answer: Only the absolute temperatures of the hot and cold reservoirs
Carnot efficiency = 1 − (Tc/Th) where Tc and Th are the absolute temperatures of the cold and hot reservoirs respectively — independent of the working fluid or engine design.
Question 6: An adiabatic process is one in which:
- Temperature remains constant throughout
- No heat is exchanged between the system and its surroundings (Correct answer)
- Pressure remains constant throughout
- Volume remains constant throughout
Correct answer: No heat is exchanged between the system and its surroundings
An adiabatic process has zero heat exchange with the environment; any temperature change results solely from work done on or by the system.
Mechanical Aptitude Test Mechanical Aptitude Heat Transfer and Thermodynamics Questions and Answers 2
The First Law of Thermodynamics is best described as: