 # Energy, Work and Power

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More Lessons for High School Physics, Math Worksheets

A series of free Online High School Physics Video Lessons.

In this lesson we will learn

• the concept of energy and the conservation of energy
• how to use the work-energy theorem
• the concept of power
• how to calculate the power of a system

### Energy

Energy is best defined as the properties of an object that enables it to do work. Energy is a scalar and is usually measured in Joules. Energy is neither created nor destroyed but shared within a system, according to the law of conservation of energy, but energy can be changed from one form to another. Types of energy include potential energy, kinetic energy and mechanical energy.

Types of Energy & the Law of Conservation of Energy
Potential Energy is energy at rest.
Kinetic Energy is energy of motion.
The Law of Conservation of Energy states that energy is never created or destroyed, it can be transformed from one type of energy to another.
Types of energy: Mechanical, Radiant (or electromagnetic), Sound, Gravitational, Chemical, Heat or Thermal.
Conservation of Energy
This video explains how energy can neither be created nor destroyed but may be transferred. Energy comes in many forms (including chemical, mechanical, light, electrical, and thermal)

### Work - Energy Theorem

According to the work-energy theorem, the net work on an object causes a change in the kinetic energy of the object.
The formula for net work is net work = change in kinetic energy = final kinetic energy - initial kinetic energy.
A brief overview of energy, kinetic energy, gravitational potential energy, and the work-energy theorem for algebra-based physics students.
Example:
The diagram represents a 155-newton box on a ramp. Applied force F causes the box to slide from point A to point B. What is the total amount of gravitational potential energy gained by the box?
How to apply the work energy theorem?
This video illustrates the work-energy theorem to solve a motion problem.
Example:
Nellie rides her bike at velocity v along a straight road and when she notices part of the road ahead missing, she applies her brakes. The friction between her tires and the road is half the weight of her and the bicycle. How far will she skid?

### Power

Power is the rate at which work is done. It is related to energy, which is the quantity used to measure work. Power can be calculated by the ratio power = work / time and is usually measured in Watts (1 Watt = 1 Joule/second).
Understanding the concept of power
High School Physics - Electrical Energy and Power
Example 1: A 110-volt toaster oven draws a current of 6 amps on its highest setting as it converts electrical energy to thermal energy. What is the toaster's maximum power rating?
Example 2: An electric iron operating at 120 volts draws 10 amps of current. How much heat energy is delivered by the iron in 30 seconds?
Example 3: What is one watt equivalent to?
Example 4: A potential drop of 50 volts is measured across a 250-ohm resistor. What is the power developed in the resistor? A brief overview of power in an algebra-based physics course
Define power. Calculate the power of a system.
Example 1: Rob and Peter move a sofa 3 meters across the floor by applying a combined force of 200N horizontally. If it takes them 6 seconds to move the sofa, what amount of power did they supply?
Example 2: Kevin then pushes the same sofa 3 meters across the floor by applying a force of 200N. Kevin, however, takes 12 seconds to push the sofa. What amount of power did Kevin supply?
Example 3: Motor A lifts a 5000N steel crossbar upward at a constant 2 m/s. Motor B lifts a 4000N steel support upward at a constant 3 m/s. Which motor is supplying more power?
Example 4: A 70-kilogram cyclist develops 210 watts of power while pedaling at a constant velocity of 7 meters per second east. What average force is exerted eastward on the bicycle to maintain this constant speed?

Try the free Mathway calculator and problem solver below to practice various math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.  