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An object has a constant velocity of 50 m/s and travels for 10 s. What is the acceleration of the object?
- A. 0 m/s²
- B. 5 m/s²
- C. 60 m/s²
- D. 500 m/s²
Correct Answer: A
Rationale: The acceleration of an object is defined as the rate of change of its velocity. When an object has a constant velocity, it means there is no change in its speed or direction. In this case, the object maintains a constant velocity of 50 m/s for 10 seconds, which implies that there is no change in velocity. Therefore, the acceleration of the object is 0 m/s² as there is no acceleration or deceleration happening. Choices B, C, and D are incorrect because acceleration is the change in velocity over time, and in this scenario of constant velocity, the acceleration is 0 m/s².
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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.
Which property of a substance does not change with a change in temperature?
- A. Mass
- B. Volume
- C. Phase
- D. Solubility
Correct Answer: A
Rationale: Mass is an intrinsic property of a substance that remains constant regardless of temperature changes. It is a measure of the amount of matter in an object, and this quantity does not vary with temperature or the environment in which the substance is located. The conservation of mass in chemistry dictates that mass is neither created nor destroyed, making it independent of temperature variations.\nVolume, on the other hand, changes with temperature due to thermal expansion or contraction. Phase can change with temperature, leading to transitions between solid, liquid, and gas states. Solubility is affected by temperature changes as it influences the ability of a substance to dissolve in a solvent.
Marilyn is driving to a wedding. She drives 4 miles south before realizing that she left the gift at home. She makes a U-turn, returns home to pick up the gift, and sets out again driving south. This time, she drives 1 mile out of her way to pick up a friend. From there, they continue 5 miles more to the wedding. Which of these statements is true about Marilyn's trip?
- A. The displacement of her trip is 6 miles, and the distance traveled is 6 miles.
- B. The displacement of her trip is 14 miles, and the distance traveled is 14 miles.
- C. The displacement of her trip is 8 miles, and the distance traveled is 14 miles.
- D. The displacement of her trip is 6 miles, and the distance traveled is 14 miles.
Correct Answer: C
Rationale: Marilyn's displacement is calculated based on her final position relative to the starting point. She drives 1 mile to pick up her friend, then 5 miles more to the wedding, totaling 6 miles after returning to her home. So, the correct displacement is 8 miles south from her starting point (4 miles to the gift + 4 miles return + 1 mile to the friend + 5 miles to the wedding). The total distance traveled is 14 miles (adding all the distances). Choice A is incorrect because it miscalculates the displacement. Choice B is incorrect as it overestimates both the displacement and distance traveled. Choice D is incorrect as it underestimates the displacement.
The Prandtl number (Pr) is a dimensionless property relating:
- A. Viscosity and thermal diffusivity
- B. Density and pressure
- C. Surface tension and pressure
- D. Reynolds number and flow regime
Correct Answer: A
Rationale: The Prandtl number (Pr) is a dimensionless number used to characterize fluid flow. It is the ratio of momentum diffusivity to thermal diffusivity. In simpler terms, it relates the ability of a fluid to conduct heat to its ability to conduct momentum. Therefore, the correct relationship is between viscosity and thermal diffusivity, making choice A the correct answer. Choices B, C, and D are incorrect because they do not represent the properties that the Prandtl number relates.
When a crane hoists a massive object at a constant velocity compared to lifting the same object gradually, the work done by the crane is:
- A. Less
- B. More
- C. Identical
- D. Dependent on the object's mass
Correct Answer: C
Rationale: The work done by the crane is identical in both scenarios. Work is defined as the force applied over a distance. Since the force needed to lift the object is equal to its weight and the displacement is the same, the work done is identical, whether the object is lifted gradually or at a constant velocity. Choice A is incorrect because the work done is the same in both cases. Choice B is incorrect as well since the work done does not increase. Choice D is incorrect as the mass of the object does not affect the work done by the crane in this scenario.