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# Kinetic and Potential Energy PowerPoint PPT Presentation

Kinetic and Potential Energy. Chapter 11. Definitions:. Kinetic Energy – energy of motion Formula:KE = 1/2mv 2 Units of KE =the joule m = mass in kg v = velocity in m/s. Potential Energy – energy of position, or stored energy Formula: Ug = mgh Units of Ug are the joule

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

• 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

### 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.

### Here we go again…

Reference level

start

finish

• 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?

• a. 208,250 J

• b. -98,000 J

A

B

C

A

B

C

### 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!