calculating energy

• kinetic energy


  Ek = 1/2 mv ²

  • m = mass (kg)
  • v = speed (m/s)
  • Ek = kinetic energy (joules, J)
• elastic potential


  the type of energy stored in a spring when it is stretched

  Ee = 1/2 ke ²

  • Ee = elastic potential energy (joules, J)
  • k = spring constant (newtons per metre, N/m)
  • e = extension (metres, m)
• gravitational potential energy


  Ep = mgh

  • Ep = gravitational potential energy (joules, J)
  • g = gravitational field strength (newtons per kilogram, N/kg)
  • h = height (metres, m)
  • m = mass (kg)
• specific heat capacity


  the energy required to raise the temp. of 1 kg of a substance by 1 °C

  -energy = mass x specific heat capacity x temp. change

  -ΔE = mcΔT

  • ΔE = change in thermal energy (joules, J)
  • m = mass (kg)
  • c = specific heat capacity (joules per kilogram per degree celsius, Jkg°C)
  • ΔT = temp. change (degrees celsius, °C)
• power - rate at which energy is transferred or the rate at which work is done


  -power = energy transferred / time

  OR

  -power = work done / time

  -p = E / t

  OR

  -p = W / t

  • P = power (watts , W)
  • E = energy transferred (joules, J)
  • t = time (seconds, s)
  • W = work done (joules, J)

  an energy transfer of 1 joule per second = power of 1 watt