1. BC Science Connections 10
Topic 3.3: Calculating Mechanical Kinetic Energy and Gravitational Potential Energy

2. Thought problem
You’re at a carnival and want to win the milk jug ball toss. If you could choose to bring your own ball, what would you bring to guarantee your success? Why?
How would you toss this ball?

3. Different physical quantities contribute to different forms of energy.
Knowing such quantities allows us to describe many forms of energy mathematically.

4. Energy of objects in MOTION.
Kinetic Energy
Energy of objects in MOTION.
where m = mass (kg)
v = velocity (m/s)
(the speed at which the object is moving)

5. Example 1
A 1.0 kg rock is fired from a catapult with a velocity of 10.0 m/s. What is its kinetic energy?

6. Calculating Energy
Energy (and subsequently work) is measured in Joules (J), named after James Prescott Joule, an English physicists.
1 Joule is equivalent to 1

7. Energy STORED in a body due to its height
Potential Energy
Energy STORED in a body due to its height
where m = mass (kg)
g = acceleration due to gravity, 9.8 m/s2
h = height (m)

8. Example 2
What is the potential energy stored in a 40.0 kg monkey hanging from a tree branch that is 15 m high?

9. A 45 kg boulder is sitting on a cliff that is 125 m high.
Example 3
A 45 kg boulder is sitting on a cliff that is 125 m high.
How much gravitational potential energy does the boulder have with respect to the bottom of the cliff?

10. Example 3 (cont’d)
How much gravitational potential energy would the boulder have if it was sitting 28 m from the top?

11. Example 3 (cont’d)
If the boulder rolls off the cliff and falls to the ground, at what velocity will it be falling just before it hits the ground? Ignore air resistance.

12. In conclusion…
What physical quantities affect (a) mechanical kinetic energy and (b) gravitational potential energy?
Mass and velocity
Mass and height (above reference point)