when a gas is compressed isothermally we can say that
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HESI A2

HESI A2 Physics Practice Test

1. When a gas is compressed isothermally, we can say that:

Correct answer: D

Rationale: When a gas is compressed isothermally, the surroundings perform work on the gas. In this process, since the temperature remains constant (isothermal), the internal energy of the gas does not change. Therefore, the correct answer is that the surroundings perform work on the gas, and its internal energy decreases. Choices A, B, and C are incorrect because they incorrectly describe the direction of work and the change in internal energy during an isothermal compression.

2. Which object below has the same density?

Correct answer: A

Rationale: Density is calculated by dividing the mass of an object by its volume. The density of object A is 6.5 g / 16.25 cm3 = 0.4 g/cm3. The density of object B is 80 g / 32 cm3 = 2.5 g/cm3. The density of object C is 48 g / 22 cm3 = 2.18 g/cm3. The density of object D is 100 g / 250 cm3 = 0.4 g/cm3. Objects A and D have the same density of 0.4 g/cm3. Therefore, the correct answer is A as it has the same density as object D, making them the only objects with a density of 0.4 g/cm3.

3. When a fluid flows past a solid object, a thin layer of fluid adheres to the object's surface due to:

Correct answer: C

Rationale: The boundary layer effect occurs when a thin layer of fluid near the surface of a solid adheres to it due to viscosity. This layer experiences a velocity gradient as the fluid farther from the surface moves faster, while the fluid closest to the surface is nearly stationary.

4. The speed of sound in dry air at 20°C is 343 m/s. If the wavelength of a sound wave is 5 m, what is its frequency?

Correct answer: C

Rationale: The speed of sound (v) can be calculated using the formula: v = f × λ, where f is the frequency and λ is the wavelength. Given that the speed of sound is 343 m/s and the wavelength is 5 m, we can rearrange the formula to solve for frequency: f = v / λ = 343 / 5 = 68.6 Hz. Therefore, the correct frequency is 68.6 Hz. Choices A, B, and D are incorrect as they do not result from the correct calculation based on the given values.

5. What characterizes laminar flow?

Correct answer: A

Rationale: Laminar flow is characterized by the smooth, parallel movement of fluid particles along layers in a predictable manner. This flow regime occurs at low velocities and is in contrast to turbulent flow, where fluid particles exhibit erratic and chaotic motion. The viscosity of the fluid does not hinder laminar flow; instead, it influences the resistance to flow. Incompressibility is a property of fluids but does not specifically define laminar flow. Therefore, the correct answer is A as it accurately describes the behavior of fluid particles in laminar flow, making B, C, and D incorrect.

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