Nokea
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.
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A car, starting from rest, accelerates at 10 m/s² for 5 seconds. What is the velocity of the car after 5 seconds?
- A. 2 m/s
- B. 5 m/s
- C. 50 m/s
- D. The answer cannot be determined from the information given.
Correct Answer: C
Rationale: The velocity of an object can be calculated using the formula: final velocity = initial velocity + (acceleration time). In this case, the car starts from rest, so the initial velocity is 0 m/s. Given that the acceleration is 10 m/s² and the time is 5 seconds, we can plug these values into the formula to find the final velocity: final velocity = 0 m/s + (10 m/s² 5 s) = 0 m/s + 50 m/s = 50 m/s. Therefore, the velocity of the car after 5 seconds is 50 m/s. Choice A (2 m/s) and Choice B (5 m/s) are incorrect because they do not consider the acceleration the car undergoes over the 5 seconds, resulting in a final velocity greater than both. Choice D (The answer cannot be determined from the information given) is incorrect as the final velocity can be determined using the provided data and the kinematic equation.
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.
According to the law of conservation of energy, energy:
- A. Can be created or destroyed
- B. Can be created, but not destroyed
- C. Can be destroyed, but not created
- D. Cannot be created or destroyed
Correct Answer: D
Rationale: The correct answer is D: 'Cannot be created or destroyed.' The law of conservation of energy states that energy cannot be created or destroyed; it can only be transformed from one form to another. This principle is a fundamental concept in physics and is supported by numerous observations and experiments. Choices A, B, and C are incorrect because they do not align with the law of conservation of energy. Energy is a conserved quantity, meaning its total amount remains constant over time, even though it can change forms.
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 Nâ‹…m
- C. 45 W
- D. 45 Nâ‹…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 Nâ‹…m. Therefore, the correct answer is 45 Nâ‹…m. Choice A (5 W) is incorrect because work is measured in joules (J) or newton-meters (Nâ‹…m), not in watts (W). Choice B (5 Nâ‹…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 (Nâ‹…m).
Longitudinal waves have vibrations that move ___________.
- A. at right angles to the direction of the vibrations
- B. in the direction opposite to that of the wave
- C. in the same direction as the wave
- D. in waves and troughs
Correct Answer: C
Rationale: In longitudinal waves, the vibrations of particles occur in the same direction as the wave propagates. This means the particles move back and forth in the direction of the wave, creating compressions and rarefactions along the wave. Therefore, the correct choice is C, in the same direction as the wave. Choice A is incorrect because transverse waves, not longitudinal waves, have vibrations at right angles to the direction of wave propagation. Choice B is incorrect as it describes the motion in transverse waves. Choice D is incorrect as it is an inaccurate representation of how longitudinal waves propagate.