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Kinetic and Potential EnergyPowerPoint Presentation

Kinetic and Potential Energy

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### Kinetic and Potential Energy

Chapter 11

Definitions:

- Kinetic Energy – energy of motion
- Formula: KE = 1/2mv2
- Units of KE =the joule
- m = mass in kg
- v = velocity in m/s

- Formula: KE = 1/2mv2

- Potential Energy – energy of position, or stored energy
- Formula: Ug = mgh
- Units of Ug are the joule
- m = mass in kg
- g = gravity (9.8 m/s2)
- h = height in meters

- Formula: Ug = mgh

Other things…

- With potential energy, the reference level is important. Remember, you may not always start off at 0 meters.
- Velocity is what affects KE the most. Why? Look at the formula…
- Height is what determines potential energy. Should the mass or gravity of an object change?

Other things continued…

- An object has the most KE when it is moving the (fastest/slowest)?
- Ug will be greatest when an object is (highest/lowest) and (moving/not moving)?
- Energy is conserved. This means energy is converted from KE to Ug and vice-versa.

Example 1

- A 90 kg rock climber climbs 45 m up to the top of a hill. He then walks 85 m from the top of the hill to the bottom. If the initial height is the reference level, find the Ug at the top of the hill and at the bottom.

- At the top:
- m = 90 kg
- g= 9.8 m/s2
- h = 45 m
- Ug = mgh
- Ug = 90 x 9.8 x 45
- Ug = 39,690 J

- At the bottom:
- m= 90 kg
- g= 9.8 m/s2
- h= 40 m ????
- Ug = mgh
- Ug = 90 x -9.8 x 40
- Ug = -35,280 J

Example 2

- A 50 kg artillery shell is shot from a cannon at Earth’s surface to a height of 425 m.
- What is the gravitational potential energy of the system when the shell is at this height?
- What is the change in potential energy when it falls to a height of 225 m?

Answers…

- a. 208,250 J
- b. -98,000 J

Classwork

p. 269

#’s 38- 40, 42, 46-49

- Converting km/hr to m/s : multiply by 1000 then divide by 3600?
- Use F = ma to find mass
- Quiz Thursday!

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