Energy Basics

Kinetic

Energy

Basics

Concept & Math Overview

First, let's recap...

What do we know so far?

Multiple Choice

What is potential energy?

• Energy of a system in motion.

• A construct representing a conserved quantity.

• Energy stored in an object due to position.

• None of these.

Multiple Choice

How much energy does a 12 kg rock have if it is suspended 5 m above the ground on earth, where g = 9.81 m/s².

• 588.6 J

• 60 J

Let's solve that last one...

mass = 12 kg

height = 5 m

g = 9.81 m/s²

We can use the equation for gravitational potential energy (PE_g) since the object is held in the air, so gravity is acting on it.

PE_g = m • g • h = 12 • 9.81 • 5 = 588.6 J

Now, let's take some notes.

Please write down the info in the next few slides.

What is Kinetic Energy?

Kinetic Energy is the energy of a system or object that is in motion.

--> Motion is REQUIRED in order to have KE.

--> It is measured in Joules (J) like all other types of energy and work.

KE = ¹/₂ m • v²

You need BOTH mass and velocity (motion)

to have kinetic energy.

Let's do an example.

You don't have to copy this one down.

A car travels at 20 m/s down the street. If it has a mass of 2000 kg, what energy is it carrying?

v = 20 m/s

m = 2000 kg

KE = 1/2 m v²

= 1/2 • 2000 • 20² = 1000 • 400

= 400,000 J

Let's review...

Multiple Choice

Which quantities are necessary to find the kinetic energy of an object?

• height, mass

• mass, gravity

• height velocity

• mass, velocity

Multiple Choice

What is the energy of a 10 kg ball that rolls along the ground at a speed of 3 m/s?

• 90 J

• 45 J

• 294.3 J

• 30 J

Multiple Select

Which of the following make up the total mechanical energy in a system?

• heat

• potential energy

• chemical energy

• kinetic energy

• electric energy

Thank you!

Galán