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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?
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