Nokea
What is the kinetic energy of a 500-kg wagon moving at 10 m/s?
- A. 50 J
- B. 250 J
- C. 2.5 10^4 J
- D. 5.0 10^5 J
Correct Answer: C
Rationale: The formula for calculating kinetic energy is KE = 0.5 mass velocity². Given the mass of the wagon is 500 kg and the velocity is 10 m/s, we can substitute these values into the formula: KE = 0.5 500 kg (10 m/s)² = 0.5 500 kg 100 m²/s² = 25,000 J or 2.5 10â´ J. Therefore, the kinetic energy of the 500-kg wagon moving at 10 m/s is 2.5 10â´ J. Choice A (50 J) is incorrect because it is too low; Choice B (250 J) is incorrect as it does not match the correct calculation; Choice D (5.0 10^5 J) is incorrect as it is too high. The correct answer is C (2.5 10^4 J).
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Fluid dynamics is a subfield of fluid mechanics concerned with:
- A. Equilibrium properties of fluids at rest (Fluid Statics)
- B. The motion and behavior of fluids under various conditions
- C. Phase transitions of fluids between liquid, gas, and solid states
- D. Engineering applications of fluids (related but broader than fluid dynamics)
Correct Answer: B
Rationale: Fluid dynamics is the study of fluids in motion and their behavior under different conditions, including how they flow, mix, and interact with their surroundings. It focuses on the dynamic aspects of fluids rather than their static properties when at rest, which is the realm of fluid statics. Phase transitions of fluids between liquid, gas, and solid states are more related to thermodynamics than fluid dynamics. While engineering applications involve fluid dynamics, the field itself is more specialized in studying the movement and behavior of fluids.
In a circuit with three same-size resistors wired in series to a 9-V power supply, producing 1 amp of current, what is the resistance of each resistor?
- A. 9 ohms
- B. 6 ohms
- C. 3 ohms
- D. 1 ohm
Correct Answer: C
Rationale: In a series circuit, the total resistance is the sum of the individual resistances. With a total voltage of 9 V and a current of 1 A, we can use Ohm's Law (V = I R) to find the total resistance: Total resistance = 9 V / 1 A = 9 ohms. Since the resistors are identical and wired in series, the total resistance is evenly divided among the three resistors: Resistance of each resistor = 9 ohms / 3 = 3 ohms. Thus, the resistance of each resistor is 3 ohms. Therefore, the correct answer is 3 ohms. Choice A, 9 ohms, is incorrect because this would be the total resistance of all three resistors combined in series. Choice B, 6 ohms, is incorrect as it does not account for the equal distribution of resistance in a series circuit. Choice D, 1 ohm, is incorrect as it is too low for resistors in series with a total resistance of 9 ohms.
When a fluid encounters a bluff body (e.g., a car), the flow can separate behind the object, creating a region of low pressure. This phenomenon is known as:
- A. Cavitation
- B. Boundary layer separation
- C. Bernoulli effect per se
- D. Drag crisis
Correct Answer: B
Rationale: The correct answer is B: Boundary layer separation. Boundary layer separation occurs when the flow of fluid detaches from the surface of a bluff body, leading to a low-pressure region behind the object. This separation creates a wake region with reduced pressure. Choice A, Cavitation, refers to the formation of vapor bubbles in a fluid and is not relevant in this context. Choice C, Bernoulli effect per se, does not specifically describe the phenomenon of flow separation behind a bluff body. Choice D, Drag crisis, is not the term used to describe the creation of a low-pressure region due to flow separation.
A 25-cm spring stretches to 28 cm when a force of 12 N is applied. What would its length be if that force were doubled?
- A. 31 cm
- B. 40 cm
- C. 50 cm
- D. 56 cm
Correct Answer: A
Rationale: When the 12 N force stretches the spring from 25 cm to 28 cm, it causes a length increase of 28 cm - 25 cm = 3 cm. Therefore, each newton of applied force causes an extension of 3 cm / 12 N = 0.25 cm/N. If the force is doubled to 24 N, the spring would extend by 24 N 0.25 cm/N = 6 cm more than its original length of 25 cm. Thus, the new length of the spring would be 25 cm + 6 cm = 31 cm. Choice A, 31 cm, is the correct answer as calculated. Choices B, C, and D are incorrect as they do not consider the relationship between force and extension in the spring, leading to incorrect calculations of the new length.
Jack stands in front of a plane mirror. If he is 5 feet away from the mirror, how far away from Jack is his image?
- A. 2.5 feet
- B. 3 feet
- C. 4.5 feet
- D. 5 feet
Correct Answer: D
Rationale: When Jack stands in front of a plane mirror, his image appears the same distance behind the mirror as Jack is in front of it. Therefore, if Jack is 5 feet away from the mirror, his image will also appear 5 feet behind the mirror. The total distance from Jack to his image is the sum of these distances, which equals 10 feet. Choices A, B, and C are incorrect because the image distance is not half of the total distance but the same as the object's distance from the mirror.