1. Chapter 5, Unit 2: Kinetic & Potential Energy
KEY

2. Legend Refresh & Connect Review of Work and Energy
Two Major Categories
Kinetic Energy
Potential Energy
Conservation of Energy
Elastic Potential Energy

3. Refresh and Connect The amount of Work done on an object depends on:
Force
Change in Displacement
Power is the rate at which work is done.
Name one form of energy and an example of that energy.

4. Two Major Categories

5. Two Specific Forms of Mechanical Energy
can be
Kinetic
Which is
Energy in motion
Potential
Which can be
Gravitational
Elastic

6. Kinetic Energy is to Potential Energy
The Ying to its Yang
Ying is to Yang As
Kinetic Energy is to Potential Energy

7. Kinetic Energy
𝐾𝐸= 1 2 𝑚 𝑣 2

8. Kinetic Energy = in motion
Kinetic Energy happens only when an object is moving!
The Kinetic Energy of an object depends on:
The mass (m)
The velocity (**must have) (v)

9. Scenario Practice: Identify the object that has the most Kinetic Energy and Why
Scenario a
Scenario B
Object 2 b/c it has a greater velocity
Object 2 b/c it has a greater mass
m= 100 kg
m= 50 kg
v= 5 m/s 1
v= 8 m/s 1 2
v= 8 m/s
v= 8 m/s 2
m= 100 kg
m= 100 kg

10. Using the KE Equation Equation: 𝐾𝐸= 1 2 𝑚 𝑣 2 Where:
KE Kinetic Energy
m mass
v velocity
Example Problem:
A 150 kg fat man is being chased by a 60 kg zombie. The man is running with a velocity of 3 m/s and the zombie with 4 m/s. Find the Kinetic Energy the zombie and the man.

11. Gravitational Potential Energy

12. Gravitational Potential Energy
An object’s Gravitational Potential Energy depends on:
The object’s mass (m)
The object’s height from the ground (h)
The acceleration due to gravity (g)
Gravitational Potential Energy of an object increases as its height increases.
Examples:
Sky Scraper Ride
Bungee Jumping
Jumping on a trampoline

13. Practice: Circle the one that has the most Gravitational Potential Energy
Scenario 1
Scenario 2
Balloon 2 b/c it has a greater mass
Skier b/c it has a greater height 1 2

14. Using the GPE Equation Equation: 𝑃 𝐸 𝑔 =𝑚𝑔ℎ Where:
PE Potential Energy
m mass
g acceleration due to gravity
h height; distance from Zero
Example Problem:
The tower of terror in Disney World is 60 m tall. If the mass of the ride is 453 kg including its passengers, what is the potential energy of the ride before it begins its descent downwards?
𝑚=453
𝑔=10 𝑚 𝑠 2
h=60 m
𝑃 𝐸 𝑔 =?
𝑃 𝐸 𝑔 =𝑚𝑔ℎ
𝑃 𝐸 𝑔 =
𝑃 𝐸 𝑔 = 𝐽

15. Elastic Potential Energy

16. Elastic Potential Energy
Elastic potential energy is resulted from stretching or compressing an object; depends on distance compresses or stretched
Examples:
Rubber Bands
Springs
Resistance Band
Equation:
𝑃 𝐸 𝑒𝑙𝑎 = 1 2 𝑘 (∆𝑥 2 )
Where:
𝑃 𝐸 𝑒𝑙𝑎 →𝐸𝑙𝑎𝑡𝑖𝑐 𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦=[𝐽]
𝑘→𝑠𝑝𝑟𝑖𝑛𝑔 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡=[N/m]***
𝑥→𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑒𝑑 𝑜𝑟 𝑠𝑡𝑟𝑒𝑡𝑐ℎ𝑒𝑑

17. Elastic Potential Practice Problem
A 9 year old boy has a crush on a girl in his class. To get her attention he takes off on the rubber bands on his braces and stretches it back .03m. Calculate t the elastic potential energy of the rubber band before the boy releases is the spring constant equals 120 N/m.
𝑃 𝐸 𝑒𝑙𝑎 =?
𝑘=120 𝑁 𝑚
𝑥=.03𝑚
𝑃 𝐸 𝑒𝑙𝑎 = 1 2 𝑘 (∆𝑥 2 )
𝑃 𝐸 𝑒𝑙𝑎 = 1 2 (120) .03 2
𝑃 𝐸 𝑒𝑙𝑎 =0.054 𝐽

18. Conservation of Energy

19. It’s the LAW! Law of Conservation of Energy states:
Energy can neither be created nor destroyed. Instead it is converted from one form of energy to another
Aka this means the Beginning must equal the End!

20. Process of Changing from Potential to Kinetic

21. An object can have both Potential and Kinetic Energy at the same time…but that amount can change quickly

22. Identify at each point if there is KE, PE, or Both
All PE
Both but more PE
Both but more KE
All KE
All KE
All KE

23. The Math of Conservation
Initial Mechanical Energy = Final Mechanical Energy
𝑀 𝐸 𝑖 =𝑀 𝐸 𝑓
𝑃 𝐸 𝑔𝑖 + 𝐾𝐸 𝑖 =𝑃 𝐸 𝑔𝑓 + 𝐾𝐸 𝑓
𝑚𝑔 ℎ 𝑖 𝑚 𝑣 𝑖 2 =𝑚𝑔 ℎ 𝑚 𝑣 𝑓 2

24. Practice Problem #1 h=15m m=2kg g=10 m/s^2 v=? 𝑚𝑔ℎ= 1 2 𝑚 𝑣 2
Misael is standing on the 15m high roof of EHTHS with a 2 kg water balloon and sees Ms. Moody walking below. Seeing his opportunity to soak Ms. Moody he drops the balloon. Fortunately, Misael doesn’t have great aim and misses Ms. Moody and the balloon hits the ground next to her. With what velocity was the balloon moving at impact?
h=15m
m=2kg
g=10 m/s^2
v=?
𝑚𝑔ℎ= 1 2 𝑚 𝑣 2
2𝑚𝑔ℎ=𝑚 𝑣 2
2𝑔ℎ =𝑣
𝑣= 2(10)(15)
𝒗=𝟏𝟕.𝟑𝟐 𝒎/𝒔

25. Practice Problem #2 h=? m=60kg g=10 m/s^2 v=7 m/s 𝑚𝑔ℎ= 1 2 𝑚 𝑣 2
A 60kg skate boarder is rolling on a flat horizontal surface with a velocity of 7 m/s right before he begins moving up the ramp. How high up the ramp will the skate boarder reach before he begins moving back down?
𝑚𝑔ℎ= 1 2 𝑚 𝑣 2
𝑔ℎ= 1 2 𝑣 2
ℎ= 𝑣 2 𝑔 =
𝒉=𝟐.𝟒𝟓 𝒎
h=?
m=60kg
g=10 m/s^2
v=7 m/s

26. Worksheet 2: #1: 24,000 J #2: 118 W