HESI A2
HESI A2 Physics
1. A key parameter in fluid selection is specific gravity (SG). For a submerged object in a reference fluid (often water), SG = ρ_object / ρ_reference. An object with SG > 1 will:
- A. Experience a net buoyant force acting upwards
- B. Experience a net buoyant force acting downwards
- C. Remain neutrally buoyant
- D. Require knowledge of the object's volume for buoyancy determination
Correct answer: A
Rationale: When the specific gravity (SG) of an object is greater than 1, it indicates that the object is denser than the reference fluid, which is often water. According to Archimedes' principle, an object with SG > 1 will experience a net buoyant force acting upwards when submerged in the fluid. This is because the buoyant force is greater than the weight of the object, causing it to float. Therefore, the correct answer is A: 'Experience a net buoyant force acting upwards.' Objects with SG < 1 would sink as they are less dense than the fluid, while objects with SG = 1 would be neutrally buoyant, neither sinking nor floating.
2. 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.
3. In an adiabatic process, there is:
- A. No heat transfer (Q = 0) between the system and the surroundings.
- B. Isothermal compression or expansion (constant temperature).
- C. Constant pressure throughout the process (isobaric process).
- D. No change in the system's internal energy (energy is conserved according to the first law).
Correct answer: A
Rationale: In an adiabatic process, choice A is correct because adiabatic processes involve no heat transfer between the system and its surroundings (Q = 0). This lack of heat transfer is a defining characteristic of adiabatic processes. Choices B, C, and D do not accurately describe an adiabatic process. Choice B refers to an isothermal process where temperature remains constant, not adiabatic. Choice C describes an isobaric process with constant pressure, not specific to adiabatic processes. Choice D mentions the conservation of energy but does not directly relate to the absence of heat transfer in adiabatic processes.
4. As a vehicle positioned at the peak of a hill rolls downhill, its potential energy transforms into:
- A. Thermal energy
- B. Neither thermal nor kinetic energy
- C. A combination of thermal and kinetic energy
- D. Kinetic energy
Correct answer: D
Rationale: The correct answer is D: Kinetic energy. Potential energy is converted into kinetic energy as the vehicle moves downhill. Kinetic energy is the energy possessed by a moving object. Thermal energy is not produced in this scenario because the energy transformation is mainly from potential to kinetic energy, not involving heat generation. Choices A, B, and C are incorrect because the primary energy transformation in this scenario is from potential to kinetic energy, not involving thermal energy.
5. 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.
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