Power and efficiency Quiz
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5 questions, one answer each
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1. A motor does 4800 J of work in 12 s. What is its power?
- A. 0.40 W
- B. 40 W
- C. 400 W
- D. 57 600 W
2. A device has an input energy of 250 J and a useful output energy of 60 J. What is its efficiency?
- A. 24%
- B. 76%
- C. 4.2%
- D. 417%
3. A kettle has a power of 2.0 kW and is 85% efficient. How much useful energy does it deliver to the water in 3.0 minutes?
- A. 3.6 × 10⁵ J
- B. 4.2 × 10⁵ J
- C. 1.7 × 10³ J
- D. 3.1 × 10⁵ J
4. Which statement defines power?
- A. Work done per unit distance
- B. Energy transferred per unit time
- C. Force multiplied by time
- D. Energy multiplied by time
5. A crane lifts 500 kg through 8.0 m in 20 s. Its motor takes 2.5 kW. What is its efficiency?
- A. 25%
- B. 98%
- C. 78%
- D. 128%