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Two objects attract each other with a gravitational force of 12 units. If you double the mass of both objects, what is the new force of attraction between them?
- A. 3 units
- B. 6 units
- C. 24 units
- D. 48 units
Correct Answer: C
Rationale: The gravitational force between two objects is directly proportional to the product of their masses. When you double the masses of both objects, the force of attraction between them increases by a factor of 2 x 2 = 4. Therefore, the new force of attraction between the two objects will be 12 units x 4 = 24 units. Choices A, B, and D are incorrect because doubling the mass results in a quadruple increase in force, not a linear one.
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Surface tension, γ, is a property of fluids arising from:
- A. Intermolecular forces between fluid molecules
- B. Gravitational attraction
- C. Viscous dissipation
- D. Pressure differentials within the fluid
Correct Answer: A
Rationale: Surface tension, represented by symbol γ, is caused by the cohesive forces between molecules in a liquid. These intermolecular forces, such as Van der Waals forces, hydrogen bonding, and dipole-dipole interactions, create a 'skin' at the surface of the liquid, giving rise to the property of surface tension. Gravitational attraction, viscous dissipation, and pressure differentials within the fluid do not directly contribute to surface tension. Therefore, the correct answer is A.
A solenoid is a long, tightly wound coil of wire that acts like a bar magnet when current flows through it. The magnetic field lines inside a solenoid are most similar to the field lines around:
- A. A single straight current-carrying wire
- B. A horseshoe magnet
- C. A permanent bar magnet
- D. A flat sheet conductor
Correct Answer: C
Rationale: The magnetic field lines inside a solenoid resemble the field lines around a permanent bar magnet. Both a solenoid and a bar magnet have north and south poles, resulting in a similar pattern of magnetic field lines. A single straight current-carrying wire produces a different field pattern because it has no coil structure like a solenoid. A horseshoe magnet has a unique field shape due to its pole arrangement, different from the uniform field pattern of a solenoid. A flat sheet conductor does not exhibit the same magnetic field characteristics as a solenoid, as it lacks the coil shape and alignment of a solenoid's magnetic field.
Which substance would be most affected by a change in temperature?
- A. Liquid nitrogen
- B. Salt crystals
- C. Hydrogen gas
- D. Iron filings
Correct Answer: C
Rationale: Hydrogen gas would be most affected by a change in temperature because gases have a greater expansion or contraction in volume with changes in temperature compared to liquids or solids. When the temperature of hydrogen gas increases, its molecules gain kinetic energy and move faster, causing the gas to expand and its volume to increase. Conversely, when the temperature decreases, the gas molecules lose kinetic energy and move slower, leading to a decrease in volume. This property makes hydrogen gas highly sensitive to temperature changes compared to liquid nitrogen, salt crystals, or iron filings. Liquid nitrogen, salt crystals, and iron filings are less affected by temperature changes because their particles are closer together and have lower kinetic energy, resulting in minimal volume changes with temperature fluctuations.
Which of the following describes a vector quantity?
- A. 5 miles per hour due southwest
- B. 5 miles per hour
- C. 5 miles
- D. None of the above
Correct Answer: A
Rationale: A vector quantity is characterized by both magnitude and direction. In the provided options, choice A, '5 miles per hour due southwest,' fits this definition as it includes both the magnitude (5 miles per hour) and the direction (southwest), making it a vector quantity. Choices B and C only provide the magnitude without indicating any direction, hence they do not represent vector quantities.
A closed system undergoes a cyclic process, returning to its initial state. What can be said about the net work done (Wnet) by the system over the entire cycle?
- A. Wnet is always positive.
- B. Wnet is always negative.
- C. Wnet can be positive, negative, or zero.
- D. Wnet is equal to the total heat transferred into the system (dQ ≠0 for a cycle).
Correct Answer: C
Rationale: For a closed system undergoing a cyclic process and returning to its initial state, the net work done (Wnet) over the entire cycle can be positive, negative, or zero. This is because the work done is determined by the area enclosed by the cycle on a P-V diagram, and this area can be above, below, or intersecting the zero work axis, leading to positive, negative, or zero net work done. Choice A is incorrect because Wnet is not always positive; it depends on the specific path taken on the P-V diagram. Choice B is incorrect as Wnet is not always negative; it varies based on the enclosed area. Choice D is incorrect because Wnet is not necessarily equal to the total heat transferred into the system; it depends on the specifics of the cycle and is not a direct relationship.