Nokea
In an adiabatic process, there is:
- A. No heat transfer (Q = 0) between the system and the surroundings.
- B. Isothermal compression or expansion (constant temperature).
- C. Constant pressure throughout the process (isobaric process).
- D. No change in the system's internal energy (energy is conserved according to the first law).
Correct Answer: A
Rationale: In an adiabatic process, choice A is correct because adiabatic processes involve no heat transfer between the system and its surroundings (Q = 0). This lack of heat transfer is a defining characteristic of adiabatic processes. Choices B, C, and D do not accurately describe an adiabatic process. Choice B refers to an isothermal process where temperature remains constant, not adiabatic. Choice C describes an isobaric process with constant pressure, not specific to adiabatic processes. Choice D mentions the conservation of energy but does not directly relate to the absence of heat transfer in adiabatic processes.
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The operating principle of a metal detector relies on:
- A. The static presence of a permanent magnet
- B. The electromotive force induced by a changing magnetic field
- C. The high electrical conductivity of most metals
- D. The unique thermal signature of metallic objects
Correct Answer: B
Rationale: The correct answer is B. Metal detectors work based on the principle of electromotive force induced by a changing magnetic field. When a metal object comes into contact with the detector's magnetic field, it disrupts the field, inducing a current in the metal that can be detected. This principle allows metal detectors to identify the presence of metallic objects without relying on the static presence of a permanent magnet, the high electrical conductivity of metals, or the thermal signature of the objects. Choice A is incorrect because metal detectors do not rely on a static magnet but on the interaction of metals with a changing magnetic field. Choice C is incorrect because while metals do have high electrical conductivity, this is not the principle underlying metal detectors. Choice D is incorrect because metal detectors do not operate based on the thermal signature of objects, but rather on their interaction with magnetic fields.
An object with a charge of 4 μC is placed 1 meter from another object with a charge of 2 μC. What is the magnitude of the resulting force between the objects?
- A. 0.04 N
- B. 0.072 N
- C. 80 N
- D. 8 10−6 N
Correct Answer: A
Rationale: To find the magnitude of the resulting force between two charges, we can use Coulomb's law, which states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. The formula for Coulomb's law is:
F = k (|q1 q2| / r²),
where F is the force, k is the Coulomb constant, q1 and q2 are the charges, and r is the distance between the charges. Substituting the given values into the formula:
F = (9 10â¹ N·m²/C²) ((4 10â»â¶ C) (2 10â»â¶ C) / (1 m)²) = 0.04 N.
Therefore, the magnitude of the resulting force between the objects is 0.04 N.
The buoyant force, F_b, experienced by an object submerged in a fluid is given by:
- A. F_b = W, the object's weight
- B. F_b = W_d, the weight of the fluid displaced by the object
- C. F_b = Ï, the density of the fluid
- D. F_b = V, the object's volume
Correct Answer: B
Rationale: The correct formula for the buoyant force experienced by an object submerged in a fluid is given by Archimedes' principle, which states that the buoyant force is equal to the weight of the fluid displaced by the object. This is represented by the formula F_b = W_d, where W_d is the weight of the fluid displaced by the object. This force acts in the opposite direction to gravity and is responsible for objects floating or sinking in fluids. Choice A is incorrect because the buoyant force is not equal to the object's weight. Choice C is incorrect because the density of the fluid is not directly related to the buoyant force. Choice D is incorrect because the object's volume is not the determining factor for the buoyant force.
A 10-kg object moving at 5 m/s has an impulse acted on it causing the velocity to change to 15 m/s. What was the impulse that was applied to the object?
- A. 10 kgâ‹…m/s
- B. 15 kgâ‹…m/s
- C. 20 kgâ‹…m/s
- D. 100 kgâ‹…m/s
Correct Answer: D
Rationale: Impulse is the change in momentum of an object. The initial momentum is calculated as 10 kg 5 m/s = 50 kgâ‹…m/s, and the final momentum is 10 kg 15 m/s = 150 kgâ‹…m/s. The change in momentum (impulse) is 150 kgâ‹…m/s - 50 kgâ‹…m/s = 100 kgâ‹…m/s. Therefore, the impulse applied to the object is 100 kgâ‹…m/s. Choices A, B, and C are incorrect because they do not reflect the correct calculation of the impulse based on the change in momentum of the object.
An airplane travels 500 miles northeast and then, on the return trip, travels 500 miles southwest. Which of the following is true?
- A. The displacement of the plane is 1,000 miles, and the distance traveled is 0 miles.
- B. The displacement of the plane is 1,000 miles, and the distance traveled is 1,000 miles.
- C. The displacement of the plane is 0 miles, and the distance traveled is 0 miles.
- D. The displacement of the plane is 0 miles, and the distance traveled is 1,000 miles.
Correct Answer: D
Rationale: The displacement of an object is the change in position from the starting point to the ending point, regardless of the path taken. In this case, the airplane returns to its original position after traveling 500 miles northeast and then 500 miles southwest. Therefore, the displacement is 0 miles. However, the distance traveled is the total path covered, which is 500 miles northeast plus 500 miles southwest, for a total of 1,000 miles. Choice A is incorrect because the displacement is not the sum of the distances traveled. Choice B is incorrect as it incorrectly states that both the displacement and the distance traveled are 1,000 miles. Choice C is incorrect as it states that both the displacement and the distance traveled are 0 miles, which is not the case.