Power and efficiency Quiz
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5 questions, one answer each
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1. A motor transfers 3600 J in 2.0 minutes. What is its power?
- A. 30 W
- B. 1800 W
- C. 7200 W
- D. 0.033 W
2. A machine has an input power of 800 W and wastes 200 W. What is its efficiency?
- A. 25%
- B. 75%
- C. 80%
- D. 200%
3. Which statement about efficiency is correct?
- A. It has units of watts
- B. It can be greater than 100% in a very good machine
- C. It is the ratio of useful output to total input
- D. It is the ratio of wasted energy to useful energy
4. A lift raises a 500 kg load through 6.0 m in 10 s. What is the useful power output?
- A. 3.0 kW
- B. 29 kW
- C. 0.29 kW
- D. 2.9 kW
5. A device wastes energy as thermal energy. Which statement is correct?
- A. Energy has been destroyed
- B. The total energy is conserved, as it is transferred to the surroundings
- C. The input energy is less than the output energy
- D. The efficiency is 100%