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According to the law of conservation of energy, energy:
- A. Can be created or destroyed
- B. Can be created, but not destroyed
- C. Can be destroyed, but not created
- D. Cannot be created or destroyed
Correct Answer: D
Rationale: The correct answer is D: 'Cannot be created or destroyed.' The law of conservation of energy states that energy cannot be created or destroyed; it can only be transformed from one form to another. This principle is a fundamental concept in physics and is supported by numerous observations and experiments. Choices A, B, and C are incorrect because they do not align with the law of conservation of energy. Energy is a conserved quantity, meaning its total amount remains constant over time, even though it can change forms.
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A box is moved by a 15 N force over a distance of 3 m. What is the amount of work that has been done?
- A. 5 W
- B. 5 Nâ‹…m
- C. 45 W
- D. 45 Nâ‹…m
Correct Answer: D
Rationale: Work done is calculated using the formula: Work = Force x Distance. In this case, the force applied is 15 N and the distance covered is 3 m. Thus, work done = 15 N x 3 m = 45 Nâ‹…m. Therefore, the correct answer is 45 Nâ‹…m. Choice A (5 W) is incorrect because work is measured in joules (J) or newton-meters (Nâ‹…m), not in watts (W). Choice B (5 Nâ‹…m) is incorrect as it miscalculates the work by not multiplying the force by the distance. Choice C (45 W) is incorrect because work is not measured in watts (W) but in newton-meters (Nâ‹…m).
A 50-kg box of iron fishing weights is balanced at the edge of a table. Peter gives it a push, and it falls 2 meters to the floor. Which of the following statements is true?
- A. Once the box hits the floor, it loses both its kinetic and potential energy.
- B. The box had kinetic energy only when it was balanced at the edge of the table.
- C. The box had both kinetic and potential energy after it fell.
- D. Once the box hits the floor, it loses all its kinetic energy.
Correct Answer: C
Rationale: When the box is balanced at the edge of the table, it has potential energy due to its position above the ground. As Peter gives it a push, and it falls 2 meters to the floor, the box then has both kinetic energy (due to its motion) and potential energy (due to gravity). Therefore, the correct statement is that the box had both kinetic and potential energy after it fell. Option A is incorrect because the box retains its energy forms even after hitting the floor. Option B is incorrect as the box has kinetic energy both before and after falling. Option D is incorrect as the box still possesses kinetic energy even after hitting the floor.
Which of the following describes a vector quantity?
- A. 5 miles per hour due southwest
- B. 5 miles per hour
- C. 5 miles
- D. None of the above
Correct Answer: A
Rationale: A vector quantity is characterized by both magnitude and direction. In the provided options, choice A, '5 miles per hour due southwest,' fits this definition as it includes both the magnitude (5 miles per hour) and the direction (southwest), making it a vector quantity. Choices B and C only provide the magnitude without indicating any direction, hence they do not represent vector quantities.
Four 5 V batteries are connected in series. What is the total voltage of the circuit?
- A. 5.0 V
- B. 10.0 V
- C. 15.0 V
- D. 20.0 V
Correct Answer: D
Rationale: When batteries are connected in series, their voltages add up. Therefore, the total voltage of the circuit with four 5 V batteries connected in series will be 5 V + 5 V + 5 V + 5 V = 20 V. Choices A, B, and C are incorrect because the voltages of the batteries add up in series, resulting in a total of 20 V.
For a compressible fluid subjected to rapid pressure changes, sound wave propagation becomes important. The speed of sound (c) depends on the fluid's:
- A. Density (Ï) only
- B. Viscosity (μ) only
- C. Density (Ï) and Bulk modulus
- D. Density (Ï) and Surface tension (γ)
Correct Answer: C
Rationale: In a compressible fluid, the speed of sound (c) depends on both the fluid's density (Ï) and Bulk modulus. Density affects the compressibility of the fluid, while Bulk modulus represents the fluid's resistance to compression and plays a crucial role in determining the speed of sound in a compressible medium. Viscosity and surface tension do not directly impact the speed of sound in a compressible fluid subjected to rapid pressure changes. Therefore, the correct answer is C.