HESI A2 Physics Practice Test

Correct Answer: A

Rationale: Rationale: 1. Atoms are electrically neutral, meaning they have no overall charge. 2. Electrons are negatively charged, and protons are positively charged. 3. In a neutral atom, the number of protons equals the number of electrons to balance charges. 4. Therefore, in an electrically neutral atom, the number of electrons is equal to the number of protons (Choice A). Summary: - Choice B is incorrect because protons are not always equal to neutrons in an atom. - Choice C is incorrect as the number of neutrons can vary and is not always greater than protons. - Choice D is incorrect as electrons can be equal to or greater than protons in an atom, depending on the element.

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.

Correct Answer: B

Rationale: The correct answer is B: Boundary layer separation. When a fluid encounters a bluff body, such as a car, the flow separates behind the object due to pressure differences, creating a region of low pressure. This separation of the boundary layer results in increased drag on the object. Cavitation (A) is the formation of vapor bubbles due to low pressure, not specific to bluff bodies. The Bernoulli effect (C) refers to the relationship between fluid speed and pressure, not directly related to flow separation. Drag crisis (D) is a sudden decrease in drag experienced by an object at high speeds, not directly related to flow separation behind a bluff body.

Correct Answer: A

Rationale: Rationale: An ideal fluid exhibits zero shear stress at any strain rate. This is because an ideal fluid is assumed to have no resistance to flow, resulting in no shear stress being generated regardless of the strain rate. This is a fundamental characteristic of an ideal fluid and distinguishes it from real fluids that exhibit varying levels of shear stress. Summary: - Choice A is correct as an ideal fluid exhibits zero shear stress at any strain rate. - Choice B is incorrect as it describes a Newtonian fluid which has a linear relationship between shear stress and strain rate. - Choice C is incorrect as it describes a Non-Newtonian fluid with a non-linear relationship between shear stress and strain rate. - Choice D is incorrect as it describes the temperature dependence of viscosity, which is not a defining characteristic of an ideal fluid.

Correct Answer: C

Rationale: The correct answer is C: Identical. When the crane hoists a massive object at a constant velocity, the work done is the same as lifting it gradually because work done is the force applied multiplied by the displacement in the direction of the force. Since the velocity is constant, the force applied remains constant, and the displacement is the same whether lifted gradually or at a constant velocity. Therefore, the work done is identical in both scenarios. Summary: A: Less - Incorrect. The work done is not less when hoisting a massive object at a constant velocity. B: More - Incorrect. The work done is not more when hoisting a massive object at a constant velocity. D: Dependent on the object's mass - Incorrect. The object's mass does not affect the work done in this scenario.