Peoples Physics Concepts

http://www.ck12.org Chapter 8. Energy Conservation

8.2 Kinetic Energy

• Describe kinetic energy and how to apply it.

Students will learn about kinetic energy, how and when to apply it and how to use kinetic energy

Key Equations

Kinetic energy

K=

1

2

mv^2

{

m mass (in kilograms, kg)

v speed (in meters per second, m/s)

Guidance

The energy of motion is kinetic energy, KE. Whenever an object is in motion it has kinetic energy. The faster it is

going, the more energy it has.

Example 1

You are using a sling to throw a small stone. If the sling is .5 m long and you are spinning it at 15 rad/s, how high

would the rock go if you throw it straight up?

Solution

We’ll start by setting the kinetic energy of rock to it’s gravitational potential energy at it’s maximum height and

then solving for the rock’s height.

KEi=PEf

1

2

mv^2 =mgh

h=

v^2

2 g

We still don’t know the rock’s linear velocity, but we do know the sling’s angular velocity and radius so we can put

those into the equation instead.