# Power and Efficiency

The following physics revision questions are provided in support of the physics tutorial on Power and Efficiency. In addition to this tutorial, we also provide revision notes, a video tutorial, revision questions on this page (which allow you to check your understanding of the topic) and calculators which provide full, step by step calculations for each of the formula in the Power and Efficiency tutorials. The Power and Efficiency calculators are particularly useful for ensuring your step-by-step calculations are correct as well as ensuring your final result is accurate.

Not sure on some or part of the Power and Efficiency questions? Review the tutorials and learning material for Power and Efficiency

Work, Energy and Power Learning Material
Tutorial IDTitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
5.5Power and Efficiency

## Power and Efficiency Revision Questions

1. The engine of a car produces 12000 J of energy every second. From this amount, 4500 J convert into heat, 100 J into sound energy and 200 J into light energy. What is the efficiency of the engine?

(Hint: The rest is the mechanical energy of the car)

1. 40 %
2. 60 %
3. 93.75 %
4. 72 %

2. An electric motor shows the value 2000 W stamped on its back. Its owner turns off all the other electric appliances except the motor and finds out the motor has drawn 150 000 J electrical energy from the main source in one minute. What is the efficiency of this electric motor?

1. 80 %
2. 20 %
3. 75 %
4. 1.3 %

3. A crane can lift a 1.2 t heavy object at h = 10 m in 20 s. Its input power is 10 kW. What is the crane's efficiency? (Take g = 10 N/kg. Also, 1 t = 1000 kg and 1 kW = 1000 W).

1. 50 %
2. 60 %
3. 80 %
4. 83 %

## Whats next?

Enjoy the "Power and Efficiency" practice questions? People who liked the "Power and Efficiency" practice questions found the following resources useful:

1. Practice Questions Feedback. Helps other - Leave a rating for this practice questions (see below)
2. Work, Energy and Power Physics tutorial: Power and Efficiency. Read the Power and Efficiency physics tutorial and build your physics knowledge of Work, Energy and Power
3. Work, Energy and Power Revision Notes: Power and Efficiency. Print the notes so you can revise the key points covered in the physics tutorial for Power and Efficiency
4. Check your calculations for Work, Energy and Power questions with our excellent Work, Energy and Power calculators which contain full equations and calculations clearly displayed line by line. See the Work, Energy and Power Calculators by iCalculator™ below.
5. Continuing learning work, energy and power - read our next physics tutorial: Work and Energy. Types of Energy