# Potential and Kinetic Energy - PowerPoint PPT Presentation

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## Potential and Kinetic Energy

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### Potential and Kinetic Energy What is Energy Energy is the ability to do WORK!!! Two types of energy Potential Energy Kinetic Energy Potential and Kinetic Energy ... – PowerPoint PPT presentation

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Title: Potential and Kinetic Energy

1
Potential and Kinetic Energy
2
What is Energy
• Energy
• is the ability to do WORK!!!
• Two types of energy
• Potential Energy
• Kinetic Energy

3
Potential and Kinetic Energy
4
• Animation
• http//www.teachersdomain.org/resource/hew06.sci.p
hys.maf.rollercoaster/

5
Potential Energy
• 1. Energy at rest
• 2. Stored Energy
• 3. Higher the object - greater the potential
energy

6
Potential Energy
• Which boulder has the least amount of potential
energy and Why?

7
Types of Potential Energy
• Elastic potential energy
• Energy stored by things that stretch or compress
• Gravitational potential energy (GPE)
• The amount of GPE an object has depends on its
mass, the acceleration due to gravity, and its
height above ground.

8
Quick Write Elastic Potential Energy
• Explain how this rubber band has elastic
potential energy!

9
Quick Write Potential Energy
• When is the spring having potential energy?

10
Brain Pop Movie Potential Energy
• http//glencoe.mcgraw-hill.com/sites/0078802482/st
udent_view0/brainpop_movies.html

11
Calculating potential energy
• PEg mgh or PEg Fwh
• Units
• PEg gravitational potential energy J or Nm
• m mass kg
• g acceleration due to gravity m/sec2
• h height m
• FwForce of Weight N
• NOTE Units for kinetic and potential energy are
J (joules). 1 joule 1 kg m2/sec2 1 Nm

12
FLASH CARD
13
Potential Energy Problems
• A weight lifter lifts a 120 kg mass from the
floor to a position above his head, 2.5 meters
above the floor.  What is the potential energy
expressed by the weight?
• PE m g h
PE (120)(9.8)(2.5)
PE 2940 J The potential energy of the weight is
2940 J.

14
• 2. What is the potential energy of a 90 N boat
before it falls from the top of a 30 m waterfall?
• PE ?
• Fw 90 N
• h 30 m
• PE Fwh (90 N) (30 m)
• PE 2700 N m 2700J

15
• If the acceleration on a new planet is 5.2 m/s2
and a meteor is sitting on a hilltop at 100 m
with 650 J of PE, then what is the mass of the
meteor?

16
Kinetic Energy
• 1. Energy of motion
• 2. The amount of kinetic energy an object
has depends on its mass and its velocity

17
Calculating Kinetic Energy
• KE ½ mv2
• Units
• KE kinetic energy J or Nm
• m mass kg
• v velocity m/sec

18
Example
• What is the kinetic energy of a 120 kg object
moving at 30 m/sec?
• KE ½ mv2
• m 120 kg v 30 m/sec KE?
• KE ½ (120 kg)(30 m/sec)2
• KE (60 kg)(900 m2/sec2)
• 54000 kg m2/sec2 54000 J

19
Quick Writes Kinetic Energy
• Which one has the highest KE?
• Which one has the least KE?

20
FLASH CARD
21
Brain Pop Movie Kinetic Energy
• http//glencoe.mcgraw-hill.com/sites/0078802482/st
udent_view0/brainpop_movies.html

22
Potential and Kinetic Energy Practice Problems
• 1. A 100kg rock sets at the top of a 50 m cliff.
What is the rocks potential energy?

23
• 2. A 70 kg rock is falling at 30 m/sec. What is
its kinetic energy?

24
• 3. A 315 kg object sets at the top of a 50 m
building. What is its potential energy?

25
• 4. A car has 3600 J of kinetic energy and is
going 3 m/sec. What is its mass?

26
Work
• Transfer of energy through motion.
• 2. The force must act in the same direction as
the motion.
• 3. Force exerted through a distance

27
• Example 1 Lifting a log is work.
• Log moves in the direction the force is applied
• Example 2 Carrying a log is not work.
• Log is held up, but moves forward, therefore no
work is done on the log.

28
Calculating Work
• W Fd
• Units
• W work J
• F force N
• d distance m

29
Example
• How much work is done when 87 kg mass is lifted
1.2 m?
• W F d d 1.2 m FW mg
• m 87 kg g 9.8 m/sec2
• W mgd
• W (87 kg)(9.8 m/sec2)(1.2 m)
• 1023 J

30
FLASH CARD
31
Work Practice Problems
• 1.You lift 19.0 kg of books 1.3 m. How much work
did you do?

32
• 2.A carpenter lifts a 80 kg beam 1.4 m and
carries it 9 m. How much work is done during the
lift? How much work is done on the beam during
the carry?

33
• 3.If 19.6 J are used to move 16 N object, how far
was the object moved?

34
• 4.If 1040 J are used to move a 76 N object, how
far was it moved?

35
• 5.If 763 J are used to move an object 20 m, how
much force was used?

36
• 6.If 70043 J are needed to move an object 73 m,
how much force was needed?