HESI A2
HESI A2 Physics
1. How might the energy use of an appliance be expressed?
- A. Power = energy × time
- B. Time + energy = power
- C. Energy = power × time
- D. Energy/power = time
Correct answer: C
Rationale: The energy use of an appliance can be expressed using the formula Energy = Power × Time. In this formula, Energy represents the amount of electricity consumed by the appliance, Power indicates the rate at which the appliance uses electricity (measured in watts), and Time represents the duration for which the appliance is being used (measured in hours). By multiplying the power rating of the appliance by the time it is in use, one can calculate the total energy consumed. Option C is the correct choice because it accurately represents the relationship between power, time, and energy. Choices A, B, and D present incorrect representations of the relationship between energy, power, and time, making them wrong answers.
2. An airplane travels 500 miles northeast and then, on the return trip, travels 500 miles southwest. Which of the following is true?
- A. The displacement of the plane is 1,000 miles, and the distance traveled is 0 miles.
- B. The displacement of the plane is 1,000 miles, and the distance traveled is 1,000 miles.
- C. The displacement of the plane is 0 miles, and the distance traveled is 0 miles.
- D. The displacement of the plane is 0 miles, and the distance traveled is 1,000 miles.
Correct answer: D
Rationale: The displacement of an object is the change in position from the starting point to the ending point, regardless of the path taken. In this case, the airplane returns to its original position after traveling 500 miles northeast and then 500 miles southwest. Therefore, the displacement is 0 miles. However, the distance traveled is the total path covered, which is 500 miles northeast plus 500 miles southwest, for a total of 1,000 miles. Choice A is incorrect because the displacement is not the sum of the distances traveled. Choice B is incorrect as it incorrectly states that both the displacement and the distance traveled are 1,000 miles. Choice C is incorrect as it states that both the displacement and the distance traveled are 0 miles, which is not the case.
3. 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.
4. A wave in a rope travels at 12 m/s and has a wavelength of 2 m. What is the frequency?
- A. 38.4 Hz
- B. 6 Hz
- C. 4.6 Hz
- D. 3.75 Hz
Correct answer: B
Rationale: The frequency of a wave is calculated using the formula: frequency = speed / wavelength. In this case, the speed of the wave is 12 m/s and the wavelength is 2 m. Therefore, the frequency is calculated as 12 m/s / 2 m = 6 Hz. Choice A (38.4 Hz), Choice C (4.6 Hz), and Choice D (3.75 Hz) are incorrect as they do not result from the correct calculation using the given values.
5. In fluid dynamics, the continuity equation, a fundamental principle, expresses the conservation of:
- A. Momentum
- B. Mass
- C. Energy
- D. Angular momentum
Correct answer: B
Rationale: The continuity equation in fluid dynamics is a statement of the conservation of mass, making choice B the correct answer. It states that the mass entering a system must equal the mass leaving the system, assuming no mass is created or destroyed within the system. Conservation of momentum (choice A) is related to Newton's laws of motion and is not directly expressed by the continuity equation. Conservation of energy (choice C) involves different principles like the first law of thermodynamics and is not the focus of the continuity equation. Angular momentum (choice D) is also a different concept related to rotational motion and not described by the continuity equation.
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