Nokea
A constant force is exerted on a stationary object. In this scenario, work is:
- A. Performed
- B. Not performed
- C. Partially performed
- D. Inconclusive without further information
Correct Answer: B
Rationale: Work is only done when a force causes displacement. Since the object is stationary, no displacement occurs, and therefore, no work is performed. Choice A is incorrect because work requires both force and displacement. Choice C is incorrect as there is no partial work - work is either done or not done. Choice D is incorrect as the scenario provided is clear - the object is stationary, so no work is being performed.
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Given the four wires described here, which would you expect to have the greatest resistance?
- A. 1 km of American wire gauge 1; diameter 7.35 mm
- B. 1 km of American wire gauge 2; diameter 6.54 mm
- C. 1 km of American wire gauge 3; diameter 5.83 mm
- D. 1 km of American wire gauge 4; diameter 5.19 mm
Correct Answer: D
Rationale: The wire with the greatest resistance is the one with the smallest diameter, as resistance is inversely proportional to cross-sectional area. Gauge 4 with a 5.19 mm diameter has the smallest diameter and, therefore, the greatest resistance. Choice A, B, and C have larger diameters compared to choice D, so they would have lower resistance values.
A 1,000-kg car drives at 10 m/s around a circle with a radius of 50 m. What is the centripetal acceleration of the car?
- A. 2 m/s²
- B. 4 m/s²
- C. 5 m/s²
- D. 10 m/s²
Correct Answer: A
Rationale: Centripetal acceleration is calculated using the formula a = v² / r, where v = 10 m/s and r = 50 m. Substituting these values: a = (10 m/s)² / 50 m = 100 / 50 = 2 m/s². Therefore, the correct answer is 2 m/s². Choice B, 4 m/s², is incorrect because it is not the result of the correct calculation. Choice C, 5 m/s², is incorrect as it does not match the calculated centripetal acceleration. Choice D, 10 m/s², is incorrect as it does not reflect the correct calculation based on the given values.
When a junked car is compacted, which statement is true?
- A. Its mass increases.
- B. Its mass decreases.
- C. Its density increases.
- D. Its density decreases.
Correct Answer: C
Rationale: When a junked car is compacted, its volume decreases while its mass remains the same. As a result, the car's density increases because density is mass divided by volume. Choice A is incorrect because the mass of the car remains the same. Choice B is incorrect because the mass does not decrease. Choice D is incorrect because the density increases as the volume decreases, not decreases.
The specific heat capacity (c) of a material is the amount of heat transfer (Q) required to raise the temperature (ΔT) of a unit mass (m) of the material by one degree (typically Celsius). The relationship between these quantities is described by the equation:
- A. Q = cΔT
- B. Q = mcΔT
- C. Q = c / mΔT
- D. Q = ΔT / mc
Correct Answer: A
Rationale: The correct equation relating heat transfer (Q), mass (m), specific heat capacity (c), and change in temperature (ΔT) is Q = mcΔT. This equation states that the heat transfer is equal to the product of the mass, specific heat capacity, and temperature change. Therefore, the correct answer is B, as it correctly represents this relationship. Choices C and D do not correctly represent the relationship between these quantities and are therefore incorrect.
Which of these objects has the greatest momentum?
- A. A 1,250-kg car moving at 5 m/s
- B. An 80-kg person running at 4 m/s
- C. A 10-kg piece of meteorite moving at 600 m/s
- D. A o.5-kg rock moving at 40 m/s
Correct Answer: A
Rationale: Momentum is the product of mass and velocity. The car has the highest momentum because it has the largest mass and a significant velocity.