Work, Power & Efficiency Quiz
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5 questions, one answer each
Each answer is checked as you go, with why.
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1. What is the equation for work done by a force?
- A. E = F ÷ d
- B. E = F × d
- C. E = F − d
- D. E = F + d
2. A crane lifts a load with a force of 500 N through a distance of 6 m. How much work is done?
- A. 83.3 J
- B. 506 J
- C. 3000 J
- D. 494 J
3. Which of these is NOT one of the three ways the energy of a system can be changed, according to the specification?
- A. Work done by forces
- B. Electrical equipment
- C. Heating
- D. Nuclear fusion
4. A motor transfers 900 J of energy in 15 s. What is its power output?
- A. 6 W
- B. 60 W
- C. 135 W
- D. 13500 W
5. A machine is supplied with 400 J of energy and does 100 J of useful work, the rest being dissipated as heat. What is its efficiency, and why can it never reach 100%?
- A. 25%; because some energy is always dissipated to the surroundings in real devices
- B. 400%; because more energy is created than supplied
- C. 75%; because heat is always the useful output
- D. 100%; because energy is always fully conserved as useful work