1. Kinetic and Potential Energy
- Energy can be described as the ability to produce heat or do work and can be broadly classified into two categories:
Kinetic – related to an object’s motion
Potential – related to an object’s stored energy
- In a closed system, energy is always conserved and transferred from one form to another

2. Kinetic and Potential Energy
PE = mgh
Potential Energy = mass × gravity × height
(this gives us gravitational potential energy, GPE)
Gravity = 9.8 m/s2
KE = ½ mv2  amount of work (force over a distance) needed to accelerate an object from rest to a speed of v
Kinetic Energy = ½ × mass × velocity2

3. A 60 kg cheetah sits in a tree 5 m above ground. What is its GPE?
GPE = m × g × h
= 60 kg × 9.8 m/s2 × 5 m
= 2940 J

4. An iPhone is thrown up into the air and reaches a height of 5 m
An iPhone is thrown up into the air and reaches a height of 5 m. What is its GPE if the phone weighs 1.37 N?
GPE = m × g × h
= 1.37 N × 5 m
= 6.85 J

5. Kinetic and Potential Energy
The relationship between kinetic and potential energy is:
Total Energy =
Kinetic Energy + Potential Energy

6. Relationship b/w Energy and Work
Since kinetic energy is energy of motion
kinetic energy of an object = work needed to create observed motion
As such, W = ΔKE
Or W = ½ mv22 – ½ mv12

7. Relationship b/w Energy and Work
Since potential energy is stored energy
potential energy of an object = work stored
As such, W = mgh (because F × d)

8. PE and KE Practice
1. A ball has a mass of 0.3 kg. If the ball is above the ground at a height of 2.0 m, what is its gravitational potential energy?
2. The ball falls and halfway down to the ground, it is traveling at 4.43 m/s. What is the kinetic energy of the ball at that moment?
3. What will the speed of the ball be just before it hits the ground?