Work, Energy and Power

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Work, Energy and Power

• Kinetic Energy

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Kinetic Energy

• Kinetic energy is the energy of motion. An object
  which has motion - whether it be vertical or
  horizontal motion - has kinetic energy.
• There are many forms of kinetic energy -
  vibratory (the energy due to vibratory motion),
  rotational (the energy due to rotational motion),
  and translational (the energy due to motion from
  one location to another).

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Continued

• The amount of translational kinetic energy (from
  here on, the phrase kinetic energy will refer to
  translational kinetic energy) which an object has
  depends upon two variables
• the mass (m) of the object and the speed (v) of
  the object.

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Continued

• The following equation is used to represent the
  kinetic energy (EK) of an object
• EK ½ mv2
• m mass
• v velocity
• This equation reveals that the EK of an object is
  directly proportional to the square of its speed.
  That means that if speed doubles, the EK will
  increase by a factor of four

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KE continued

• Kinetic energy is a scalar quantity it does not
  have a direction. Unlike velocity, acceleration,
  force, and momentum, the kinetic energy of an
  object is completely described by magnitude
  alone.
• Like work and potential energy, the standard
  metric units of measurement for kinetic energy is
  the Joule.

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Example 1

• Determine the kinetic energy of a 1000-kg roller
  coaster car that is moving with a speed of 20.0
  m/s.
• EK ½ mv2
• ½ (1000kg)(20.0m/s)2
• 200 000 Joules
• 2.00 x 105 Joules or 200 kJ

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Example 2

• If the roller coaster car in the above problem
  were moving with twice the speed, then what would
  be its new kinetic energy?
• EK ½ mv2
• ½ (1000kg)(40.0m/s)2
• 800 000 Joules
• 8.00 x 105 Joules or 800 kJ

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Example 3

• Missy Diwater, the former platform diver for the
  Ringling Brother's Circus had a kinetic energy of
  15kJ just prior to hitting the bucket of water.
  If Missy's mass is 50 kg, then what is her speed?
• EK ½ mv2
• 15 000 J ½ (50kg)v2
• 2(15000) 50v2
• 30000 v2
• 50
• v 24.5m/s

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Example 4

• Calculate the velocity of a fist with a mass of
  750g while being slammed into a board with a
  force of 50 N over a distance of 35 cm.(watch out
  for units!)
• EK W ½ mv2
• W F d ½ (0.75kg) v2
• 50 N x 0.35 m ½ (0.75kg) v2
• 17. 5/ 0.375 v2
• 6.83 m/s v