HESI A2
HESI A2 Physics
1. When the heat of a reaction is negative, which statement is true?
- A. The products have less energy and are less stable.
- B. The products have more energy and are more stable.
- C. The products have less energy and are more stable.
- D. The products have more energy and are less stable.
Correct answer: C
Rationale: When the heat of a reaction is negative, it indicates that the reaction releases energy in the form of heat. This means that the products have lower energy levels compared to the reactants. Lower energy levels are associated with greater stability in chemical systems. Therefore, when the heat of a reaction is negative, the products are more stable due to having less energy than the reactants. Choice A, stating that the products have less energy and are less stable, is incorrect as lower energy levels imply greater stability. Choice B, stating that the products have more energy and are more stable, is incorrect as lower energy levels lead to higher stability. Choice D, stating that the products have more energy and are less stable, is incorrect as lower energy levels are associated with higher stability.
2. A box is moved by a 15 N force over a distance of 3 m. What is the amount of work that has been done?
- A. 5 W
- B. 5 N⋅m
- C. 45 W
- D. 45 N⋅m
Correct answer: D
Rationale: Work done is calculated using the formula: Work = Force x Distance. In this case, the force applied is 15 N and the distance covered is 3 m. Thus, work done = 15 N x 3 m = 45 N⋅m. Therefore, the correct answer is 45 N⋅m. Choice A (5 W) is incorrect because work is measured in joules (J) or newton-meters (N⋅m), not in watts (W). Choice B (5 N⋅m) is incorrect as it miscalculates the work by not multiplying the force by the distance. Choice C (45 W) is incorrect because work is not measured in watts (W) but in newton-meters (N⋅m).
3. During adiabatic compression of a gas, what happens to its temperature?
- A. Remains constant
- B. Decreases
- C. Increases
- D. Becomes unpredictable without additional information
Correct answer: C
Rationale: During adiabatic compression, the gas's temperature increases. This is because no heat is exchanged with the surroundings, and all the work done on the gas results in an increase in internal energy. Choice A is incorrect because the temperature does not remain constant during adiabatic compression. Choice B is incorrect as the temperature does not decrease. Choice D is incorrect as the behavior of the gas's temperature during adiabatic compression is predictable based on the principles of thermodynamics.
4. 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 (ρ) only
- B. Viscosity (μ) only
- C. Density (ρ) and Bulk modulus
- D. Density (ρ) and Surface tension (γ)
Correct answer: C
Rationale: In a compressible fluid, the speed of sound (c) depends on both the fluid's density (ρ) 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.
5. A 110-volt hair dryer delivers 1,525 watts of power. How many amperes does it draw?
- A. 167.75 amperes
- B. 1.635 amperes
- C. 1.415 amperes
- D. 13.9 amperes
Correct answer: D
Rationale: To determine the amperes drawn by the hair dryer, we use the formula: Amperes = Watts / Volts. The hair dryer operates at 1,525 watts with 110 volts. Dividing 1,525 watts by 110 volts yields 13.9 amperes. Therefore, the correct answer is 13.9 amperes. Choices A, B, and C are incorrect because they do not result from the correct calculation using the formula.
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