Kinetic Energy


Kinetic Energy
Transparency Master

Forms of Energy - Kinetic Energy:
Activity 1 :Key

Transparency Master 		The graph shows the amount of kinetic energy (in joules) that a 60kg person would have if they were moving at speeds up to 10m/s.
  1. How much kinetic energy would a 60kg person have when running at 6m/s?
    Answer: approximately 1100 joules of kinetic energy.

  2. How much kinetic energy would a 60kg person have when jogging at 2m/s?
    Answer: approximately 120 joules of kinetic energy.

  3. How fast would a 60kg person need to run to have 500J of kinetic energy?
    Answer: approximately 4 m/s.

  4. How fast would a 60kg person need to run to have twice the kinetic energy as the person in the question above?
    Answer: approximately 5.8 m/s.

  5. A small waterfall has a flow rate of 60kg (of water) per second. The speed of the water at the bottom of the falls is 8m/s. How much energy (per second) could be extracted from this waterfall.

Answer: The kinetic energy of a body depends only on its mass and its speed, not on its direction or its composition. Therefore the kinetic energy of 60kg of water moving downwards is the same as that of a 60kg person moving horizontally.

Both would have a kinetic energy of approximately 1900J or 1.9kJ each second.

Recall that power is expressed in joules per second or watts. If the water could be brought to rest (zero speed) and all the kinetic energy exacted as electricity (without any energy being lost in the process), the waterfall would produce 1.9kW of electrical power.

Of course no energy conversion process is 100% efficient, energy being lost as heat to the environment during the transformation to electricity, so in a real electrical power plant at this waterfall, the output as electricity would be less than 1.9kW.

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