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During an isothermal (constant temperature) expansion, what is the work done by the gas on the surroundings?
- A. Positive and equal to the change in internal energy.
- B. Zero.
- C. Negative and equal to the change in internal energy.
- D. Positive and greater than the change in internal energy.
Correct Answer: D
Rationale: In an isothermal expansion, the temperature remains constant, meaning there is no change in internal energy. However, the gas still does work on the surroundings as it expands, and this work is positive. Since internal energy does not change, the correct answer is D, 'Positive and greater than the change in internal energy.' Choice A is incorrect because the work done is not equal to the change in internal energy. Choice B is incorrect as work is done during the expansion. Choice C is incorrect since the work done is not negative during an isothermal expansion.
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A circular running track has a circumference of 2,500 meters. What is the radius of the track?
- A. 1,000 m
- B. 400 m
- C. 25 m
- D. 12 m
Correct Answer: B
Rationale: The radius of a circular track can be calculated using the formula: Circumference = 2 π radius. Given that the circumference of the track is 2,500 m, we can plug this into the formula and solve for the radius: 2,500 = 2 π radius. Dividing both sides by 2π gives: radius = 2,500 / (2 3.1416) ≈ 397.89 m. Therefore, the closest answer is 400 m, making option B the correct choice. Option A (1,000 m) is too large, option C (25 m) is too small, and option D (12 m) is significantly smaller than the calculated radius.
Psychrometrics is a branch of thermodynamics that deals with the properties of:
- A. Ideal gases.
- B. Magnetic materials.
- C. Mixtures of moist air and water vapor.
- D. Nuclear reactions.
Correct Answer: C
Rationale: Psychrometrics is the study of the physical and thermodynamic properties of gas-vapor mixtures, especially mixtures of moist air and water vapor. This branch of thermodynamics focuses on the relationships between temperature, pressure, humidity, and other properties of these mixtures. Choice A, ideal gases, is incorrect because psychrometrics specifically deals with gas-vapor mixtures, not ideal gases. Choice B, magnetic materials, and Choice D, nuclear reactions, are unrelated to psychrometrics and thermodynamics, making them incorrect. Understanding psychrometrics is crucial in fields like heating, ventilation, air conditioning, and refrigeration (HVAC&R) to design systems that effectively control air quality, comfort, and temperature.
The amount of energy lost in a circuit due to electrical resistance is dissipated in the form of:
- A. Light
- B. Sound
- C. Heat
- D. Mechanical work
Correct Answer: C
Rationale: When electrical current flows through a circuit with resistance, energy is lost in the form of heat due to the resistance encountered by the electrons. This dissipation of energy as heat is a common phenomenon in electrical circuits and is known as Joule heating. Therefore, the correct answer is 'Heat.' Light, sound, and mechanical work are not typical forms in which energy is lost due to electrical resistance. Light is not a direct result of energy dissipation in electrical circuits, sound is not a form of energy dissipation in this context, and mechanical work pertains to the application of physical force and not the dissipation of energy due to resistance.
Which vehicle has the greatest momentum?
- A. A 9,000-kg railroad car traveling at 3 m/s
- B. A 2,000-kg automobile traveling at 24 m/s
- C. A 1,500-kg MINI Coupe traveling at 29 m/s
- D. A 500-kg glider traveling at 89 m/s
Correct Answer: D
Rationale: The momentum of an object is calculated by multiplying its mass by its velocity. The momentum formula is p = m v, where p is momentum, m is mass, and v is velocity. Comparing the momentum of each vehicle: A: 9,000 kg 3 m/s = 27,000 kg·m/s B: 2,000 kg 24 m/s = 48,000 kg·m/s C: 1,500 kg 29 m/s = 43,500 kg·m/s D: 500 kg 89 m/s = 44,500 kg·m/s. Therefore, the glider (500-kg) traveling at 89 m/s has the greatest momentum of 44,500 kg·m/s, making it the correct choice. Options A, B, and C have lower momentum values compared to option D, proving that the 500-kg glider traveling at 89 m/s has the highest momentum among the given vehicles.
For a compressible fluid subjected to rapid pressure changes, sound wave propagation becomes important. The speed of sound (c) depends on the fluid's:
- A. Density (Ï) only
- B. Viscosity (μ) only
- C. Density (Ï) and Bulk modulus
- D. Density (Ï) and Surface tension (γ)
Correct Answer: C
Rationale: In a compressible fluid, the speed of sound (c) depends on both the fluid's density (Ï) and Bulk modulus. Density affects the compressibility of the fluid, while Bulk modulus represents the fluid's resistance to compression and plays a crucial role in determining the speed of sound in a compressible medium. Viscosity and surface tension do not directly impact the speed of sound in a compressible fluid subjected to rapid pressure changes. Therefore, the correct answer is C.