CP7: Energy: work and power

• What is power?

  The rate of work being done or the rate at which energy is transferred
• what is the equation linking work done, force and distance?

  Work done (J) = Force (N) x Distance (M)
• What equation links power, work done and time?

  power (w) = work done (J) / time taken (s)

  P= E/t
• What is the law of conservation of energy?

  Never created or destroyed only transferred
• what is a closed system?

  a system that experiences no external forces where the total energy remains the same at all times
• what is work done?

  when an external force transfers energy to a system
• What is power?


  Rate at which energy is transferred or the rate at which work is done
• what is the equation relating power, energy and time?


  power = energy / time

  E

  P T
• what is the equation relating energy (work done),force and direction?


  work done (j) = force x distance moved

  E

  F d
• what is work done?

  a measure of entry transferred - used when a force is used to move a object by a certain distance
• what is the correlation between watts and joules?

  1 watt = 1 joule per second
• what is power, energy transferred/work done and time measured in?

  power = watts (W)

  energy transferred/ work done = joules (J)

  time = seconds (s)
• what 3 main ways can energy be transferred?

  • work done/mechanical work = force moving an object by a certain distance
  • electric work = charges moving by potential difference
  • heating = temperature difference from electricity chemical changes
• what is the rule about energy efficiency?

  it is rarely every 100% transferred
• what is the equation for efficiency?

  efficiency = useful output energy/ total input energy
• what is the equation relating kinetic energy, mass and speed?

  Kinetic energy = 1/2 x mass x velocity ^2

  KE

  1/2 M v2
• what is the equation relating gravitational potential energy, mass, gravity and height?


  Gravitational potential energy = mass x gravitational field strength x height

  GPE

  m g h
• why can mechanical processes be wasteful?

  • they get hot from friction
  • energy is dissipated through a rise in temperature
  • energy is lost to the surroundings