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Energy, Work, Power, and the Law of Conservation of Mechanical Energy

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Energy, Work, Power, and the Law of Conservation of Mechanical Energy Energy The ability of a physical system to do work on another physical system. – PowerPoint PPT presentation

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Title: Energy, Work, Power, and the Law of Conservation of Mechanical Energy


1
Energy, Work, Power, and the Law of Conservation
of Mechanical Energy
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Energy
  • The ability of a physical system to do work on
    another physical system.
  • The ability to move matter/energy
  • Energy cannot be created or destroyed
  • S.I. Units joules, kilowatt-hours, kilocalories
  • E mc2 kgm2/s2 joules

4
Forms of Energy
  • Matter (Emc²)
  • Thermal energy (thermal energy in transit is
    called heat)
  • Chemical Energy
  • Electric Energy
  • Radiant Energy (the energy of electromagnetic
    radiation, aka light)
  • Nuclear energy
  • Magnetic energy
  • Elastic energy
  • Sound energy
  • Mechanical energy
  • Luminous Energy

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Mechanical Energy
  • Sum of Potential (U) and Kinetic energy (K) of a
    system
  • Emechanical U K
  • If forces acting on a system are conservative,
    Emechanical is conserved
  • E.g. gravity, ideal spring, magnetic, and
    electric forces
  • If forces acting on a system are
    nonconservative, Emechanical can be lost as
    heat.
  • E.g. friction and air resistence

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Potential Energy (U)
  • Energy of a body or system due to it is position
    or arrangement of particles
  • E.g. Gravitational, elastic, chemical, nuclear,
    electrostatic, and magnetic.
  • Ugrav mgh kg m/s2 m J

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Kinetic Energy (K)
  • The energy of an object due to its motion
  • K ½ mv2 kg m2/s2 J

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Work
  • A force acting in a straight line through a
    distance
  • W F d Fd cos T (where T is the angle
    between F and the displacement vector)
  • N m kg m/s2 m joules
  • Work-Energy Theorem
  • W ?K K2 K1 ½ m (v22 v12)

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Power
  • The rate at which work is performed or energy is
    converted
  • Pavg ?W/ ?t J/s Watt
  • 1 Horsepower 745.7 Watts

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A kilogram of TNT contains 4.184 x 106 J of
chemical energy. If a NASCAR Sprint Cup car has
a mass of 3200lbs, how many kg worth of TNT
equivalent would it possess in kinetic energy
while travelling at 210 miles per hour?
22
  • V 210 mi/h 93.9 m/s (308 ft/s, FYI)
  • m 3200 lbs 1454.5 kg
  • K 1/2mv2 1/2 (1454.5 kg)(93.9 m/s)2
  • 6.4 x 106 J
  • 6.4 x 106 J / 4.184 x 106 J 1.53 kg
    (3.4lbs)TNT Equivalent

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If 2g of matter were converted into energy, for
how many years could you power a 100W lightbulb?
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  • Emc2 .002kg (3.0 x 108 m/s)2
  • 1.8 x 1014 J
  • Since Pavg ?Work/ ?t
  • t Work/Pavg
  • 1.8 x 1014 J / 100 Watts
  • 1.8 x 1012 s
  • 57,077 years

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