Energy, Work And Power (continued 1)
Overview
Two cranes can lift the same load to the same height, yet one finishes in seconds and the other takes a minute. They do the same work but the fast one has more power. Power is the rate of doing work, and it is what separates a sprinter from a stroller and a sports car from a scooter.
In this short but important lesson you will define power precisely, learn its two equivalent equations, and calculate it from work done or energy transferred over time. Every answer here is a number with the unit watt, so getting the substitution and units right is the whole game.
Objectives
- [Core] Understand that mechanical or electrical work done is equal to the energy transferred
- [Core] Recall and use the equation for mechanical working W = Fd = ΔE
- [Core] Describe how useful energy may be obtained, or electrical power generated, from: (a) fossil fuels (b) biofuels (c) water, including waves, tides, and hydroelectric dams (d) geothermal resources (e) nuclear fission (f) light from the Sun (solar cells) (g) infrared and other electromagnetic waves from the Sun to heat water (solar thermal collectors) (h) wind (wind turbines) including references to a boiler, turbine and generator where they are used
- [Core] Understand, qualitatively, the concept of efficiency of energy transfer
- [Supplement] Know that radiation from the Sun is the main source of energy for all our energy resources except geothermal, nuclear and tidal
- [Supplement] Know that energy is released by nuclear fusion in the Sun (detailed knowledge of the process of fusion is not required)
- [Supplement] Know that energy is released by nuclear fission in nuclear reactors (detailed knowledge of the process of fission is not required)
- [Supplement] Define efficiency as: useful energy output (a) efficiency = × 100% total energy input useful power output (b) efficiency = × 100% total power input recall and use the equations
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Energy, Work And Power (continued 1). Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Power is defined as: A. force x distance B. work done per unit time C. energy x time D. force x time Answer: B
- A motor does 4000 J of work in 20 s. Its power is: A. 80 000 W B. 200 W C. 0.005 W D. 4020 W Answer: B
- The unit of power, the watt, is equivalent to: A. 1 joule B. 1 joule per second C. 1 newton metre D. 1 newton per second Answer: B
- A 1500 W heater runs for 60 s. The energy transferred is: A. 25 J B. 1560 J C. 90 000 J D. 1500 J Answer: C
- A crane lifts a 200 N load 5 m in 10 s. The output power is: A. 100 W B. 1000 W C. 10 W D. 4 W Answer: A
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