HESI A2 Physics Practice Test

Correct Answer: A

Rationale: The correct answer is A: H = U + PV. Enthalpy (H) is defined as H = U + PV, where U is internal energy, P is pressure, and V is volume. This equation comes from the first law of thermodynamics, which states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. In this case, the work done by the system is PΔV, which represents the product of pressure and volume. Therefore, the correct relationship between enthalpy, internal energy, pressure, and volume is H = U + PV. Choices B, C, and D are incorrect because they do not accurately represent the definition of enthalpy. Choice B (H = U - PV) is incorrect because it subtracts the product of pressure and volume from internal energy, which is not the correct relationship. Choice C (H = U / PV) is incorrect because it divides internal

Correct Answer: C

Rationale: The gravitational force between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them (F = G * (m1 * m2) / r^2). When the distance is halved, the force quadruples (2^2 = 4 times). Therefore, if the original force is 12 units, when the distance is halved, the new force will be 12 * 4 = 48 units. Therefore, the correct answer is C. Choice A (3 units) is incorrect because the force increases when the distance is halved. Choice B (6 units) is incorrect as well, as the force should increase more when the distance is halved. Choice D (48 units) is incorrect because the new force of attraction is not doubled but quadrupled when the distance is halved.

Correct Answer: B

Rationale: To calculate the magnitude of the resulting force, we use Coulomb's Law: \(F = k \cdot \frac{{|q_1 \cdot q_2|}}{{r^2}}\), where \(k\) is the electrostatic constant, \(q_1\) and \(q_2\) are the charges, and \(r\) is the distance between them. Plugging in the values, we get \(F = 9 \times 10^9 \cdot \frac{{3 \times 10^{-6} \cdot 2 \times 10^{-6}}}{{(0.3)^2}} = 0.18\) N. Choice B is correct because it correctly calculates the force using Coulomb's Law. Choices A, C, and D are incorrect because they either miscalculate the force or provide unrealistic values that do not align with the physics of electrostatic forces.

Correct Answer: B

Rationale: The correct answer is B: The ratio of the potential difference between the ends of a conductor to current is a constant, R. This is in accordance with Ohm's law, which states that V (voltage) = I (current) x R (resistance). Ohm's law establishes a direct proportionality between voltage and current when resistance is constant. The constant R represents the resistance of the conductor. Option A is incorrect because voltage and current are directly proportional when resistance is constant, not inversely proportional. Option C is incorrect as voltage is not the amount of charge passing through a point per second, but rather the potential difference. Option D is incorrect as power is calculated using the formula P = VI, not I x V.

Correct Answer: A

Rationale: The Prandtl number (Pr) is defined as the ratio of momentum diffusivity (kinematic viscosity) to thermal diffusivity in a fluid. Therefore, the correct answer is A, viscosity and thermal diffusivity. This is because Pr provides a measure of the relative importance of momentum diffusivity to thermal diffusivity in a fluid flow. Choices B, C, and D are incorrect because they do not directly relate to the definition and concept of the Prandtl number. B relates to the equation of state, C relates to intermolecular forces, and D relates to flow characteristics, none of which are directly linked to the Prandtl number.