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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.
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A spring has a spring constant of 20 N/m. How much force is needed to compress the spring from 40 cm to 30 cm?
- A. 200 N
- B. 80 N
- C. 5 N
- D. 2 N
Correct Answer: D
Rationale: The change in length of the spring is 40 cm - 30 cm = 10 cm = 0.10 m. The force required to compress or stretch a spring is given by Hooke's Law: F = k x, where F is the force, k is the spring constant (20 N/m in this case), and x is the change in length (0.10 m). Substituting the values into the formula: F = 20 N/m 0.10 m = 2 N. Therefore, the correct answer is 2 N. Choice A (200 N) is incorrect because it miscalculates the force. Choice B (80 N) is incorrect as it does not apply Hooke's Law correctly. Choice C (5 N) is incorrect as it underestimates the force required.
For steady, incompressible flow through a pipe, the mass flow rate (á¹) is related to the fluid density (Ï), cross-sectional area (A), and average velocity (v) via the continuity equation:
- A. á¹ cannot be determined without additional information
- B. á¹ = ÏvA
- C. Bernoulli's principle is solely applicable here
- D. The equation of state for the specific fluid is required
Correct Answer: B
Rationale: The continuity equation for steady, incompressible flow states that the mass flow rate is the product of the fluid's density, velocity, and cross-sectional area. Hence, á¹ = ÏvA. Choice A is incorrect because the mass flow rate can be determined using the given formula. Choice C is incorrect as Bernoulli's principle does not directly relate to the mass flow rate calculation. Choice D is incorrect as the equation of state is not needed to calculate the mass flow rate in this scenario.
What is the diameter of a loop if its radius is 6 meters?
- A. 6 m
- B. 12 m
- C. 18 m
- D. 36 m
Correct Answer: B
Rationale: The diameter of a loop is calculated by multiplying the radius by 2. Since the radius is 6 meters, the diameter is 6 2 = 12 meters. Therefore, the correct answer is 12 meters. Choice A (6 m) is the radius, not the diameter. Choices C (18 m) and D (36 m) are incorrect as they do not reflect the correct calculation for determining the diameter of a loop.
A pitcher throws a 45-g baseball at a velocity of 42 meters per second. What is the ball's momentum?
- A. 0.189 kgâ‹…m/s
- B. 1.89 kgâ‹…m/s
- C. 1.07 kgâ‹…m/s
- D. 0.93 kgâ‹…m/s
Correct Answer: B
Rationale: Momentum is calculated by multiplying mass (in kg) by velocity (in m/s). The mass of the baseball is 0.045 kg (45 grams converted to kg), and the velocity is 42 m/s. Momentum = 0.045 kg 42 m/s = 1.89 kgâ‹…m/s. Therefore, the correct answer is 1.89 kgâ‹…m/s. Choice A is incorrect as it incorrectly converts the mass from grams to kg. Choice C and D are incorrect due to calculation errors.
Which of these substances is most compressible?
- A. Gold
- B. Water
- C. Mercury
- D. Methane
Correct Answer: D
Rationale: Methane, a gas at room temperature and pressure, is the most compressible substance among the options provided. Gases are generally more compressible compared to liquids and solids because their particles have more space between them, allowing for greater compression when pressure is applied. Gold, water, and mercury, being solid and liquid substances, respectively, have particles arranged closely together, making them less compressible. Therefore, the correct answer is Methane.