Nokea
The Reynolds number (Re) is a dimensionless quantity used to characterize:
- A. Fluid density
- B. Flow regime (laminar vs. turbulent)
- C. Surface tension effects
- D. Buoyancy force magnitude
Correct Answer: B
Rationale: The Reynolds number is a dimensionless quantity used to characterize the flow regime, specifically whether it is laminar (smooth) or turbulent (chaotic). It depends on the velocity of the fluid, its characteristic length (such as pipe diameter), and its viscosity. A low Reynolds number indicates laminar flow, while a high Reynolds number suggests turbulence. Choices A, C, and D are incorrect because the Reynolds number is not related to fluid density, surface tension effects, or buoyancy force magnitude.
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As a car is traveling on the highway, its speed drops from 60 mph to 30 mph. What happens to its kinetic energy?
- A. Its energy is halved.
- B. Its energy is doubled.
- C. Its energy is quadrupled.
- D. Its energy is divided by four.
Correct Answer: A
Rationale: The correct answer is A. Kinetic energy is proportional to the square of the velocity. When the speed drops from 60 mph to 30 mph, the kinetic energy is halved. Choice B is incorrect because halving the speed results in halving the kinetic energy, not doubling it. Choice C is incorrect because quadrupling the kinetic energy would require increasing the speed fourfold, not halving it. Choice D is incorrect because dividing the energy by four would imply a different relationship between speed and kinetic energy, which is not the case.
A caterpillar starts moving at a rate of 14 in/hr. After 15 minutes, it is moving at a rate of 20 in/hr. What is the caterpillar's rate of acceleration?
- A. 6 in/hr²
- B. 12 in/hr²
- C. 24 in/hr²
- D. 280 in/hr²
Correct Answer: C
Rationale: Acceleration is the change in velocity over time. The change in velocity for the caterpillar is 20 in/hr - 14 in/hr = 6 in/hr. Since this change occurred over 15 minutes (or 0.25 hours), the acceleration can be calculated as (6 in/hr) / (0.25 hr) = 24 in/hr². Therefore, the caterpillar's rate of acceleration is 24 in/hr², which corresponds to choice C. Choice A, 6 in/hr², is incorrect as it does not account for the time factor and the correct calculation. Choice B, 12 in/hr², is incorrect as it doubles the correct acceleration value. Choice D, 280 in/hr², is significantly higher than the correct value, indicating a calculation error.
An object with a mass of 45 kg has momentum equal to 180 kgâ‹…m/s. What is the object's velocity?
- A. 4 m/s
- B. 8.1 km/s
- C. 17.4 km/h
- D. 135 m/s
Correct Answer: A
Rationale: The momentum of an object is calculated by multiplying its mass and velocity. Mathematically, momentum = mass x velocity. Given that the mass is 45 kg and the momentum is 180 kgâ‹…m/s, we can rearrange the formula to solve for velocity: velocity = momentum / mass. Plugging in the values, velocity = 180 kgâ‹…m/s / 45 kg = 4 m/s. Therefore, the object's velocity is 4 m/s. Choices B, C, and D are incorrect because they do not align with the correct calculation based on the given mass and momentum values.
Viscosity, μ, is a transport property of a fluid that reflects its:
- A. Inertia
- B. Resistance to flow
- C. Compressibility
- D. Buoyancy generation
Correct Answer: B
Rationale: Viscosity refers to a fluid's resistance to flow. A fluid with high viscosity (like honey) flows slowly, while a fluid with low viscosity (like water) flows more easily. It is a measure of internal friction in the fluid. Choice A, 'Inertia,' is incorrect as inertia is the tendency of an object to resist changes in its state of motion. Choice C, 'Compressibility,' is incorrect as it refers to the ability of a fluid to be compressed. Choice D, 'Buoyancy generation,' is incorrect as it relates to the upward force exerted by a fluid that opposes the weight of an immersed object.
A 780-watt refrigerator is powered by a 120-volt power source. What is the current being drawn?
- A. 660 amperes
- B. 150 amperes
- C. 6.5 amperes
- D. 0.15 amperes
Correct Answer: C
Rationale: To calculate the current being drawn by the refrigerator, you can use the formula: Current (I) = Power (P) / Voltage (V). Given that the power of the refrigerator is 780 watts and the voltage is 120 volts, you can plug these values into the formula to find the current: I = 780 watts / 120 volts = 6.5 amperes. Therefore, the current being drawn by the 780-watt refrigerator is 6.5 amperes. Choice A, 660 amperes, is incorrect as it is significantly higher than the correct answer. Choice B, 150 amperes, is also incorrect and too high. Choice D, 0.15 amperes, is incorrect as it is too low. The correct answer is 6.5 amperes.