Efficency

• What does an energy transfer convert input energy into?


  Useful and wasted energy
• What is meant by wasted energy?


  Energy in a form that we didn't want or can't use
• In the context of a car, what is the input energy when accelerating?


  The chemical energy in its fuel
• How does a car's engine convert fuel energy?


  It burns the fuel to convert it to kinetic energy in the wheels
• What is the useful output when a car accelerates?


  An increase in kinetic energy that increases the car's speed
• What are two forms of wasted energy when a car accelerates?

  Thermal energy and sound energy
• Why is wasted energy considered a problem in energy transfers?


  It is energy we can't store or use again
• How is the efficiency of an energy transfer defined?


  As the proportion of input energy that becomes useful output energy
• What does a higher efficiency in a process indicate?


  More useful output from a given input
• If 60% of energy is converted to kinetic energy, what is the efficiency of the process?


  60%
• Why is knowing the efficiency of a process important?


  More efficient energy transfers require less input for the same output
• If a helicopter needs gravitational potential energy to raise it, what does this imply about energy transfer?


  It requires a specific energy output for a certain height
• How do two cars with different efficiencies compare in terms of input energy needed for the same kinetic energy output?


  The more efficient car needs less input energy
• How much chemical energy does the top car need to achieve 0.7 megajoules of kinetic energy?


  1 megajoule
• How much chemical energy does the bottom car need to achieve the same kinetic energy?


  2 megajoules
• What does it mean if the top car is more efficient than the bottom car?

  A greater proportion of the input energy was useful in the top car
• What are the types of energy involved in the energy transfer of a car accelerating?

  • Chemical energy (input)
  • Kinetic energy (useful output)
  • Thermal energy (wasted)
  • Sound energy (wasted)
• What are the implications of energy efficiency in vehicles?


  • More efficient vehicles require less fuel
  • They produce less wasted energy
  • They achieve the same output with lower input energy