3.3 Work, Energy and Power

• When energy is transferred work is done

  Work done is the product of the force and the distance moved in this direction

  Work done = Force * x * cos(0)

  
  

  Work done is maximum when cos(0) = 0

  Work done is minimal when cos(0) = 90
• Base units of the Joule

  W = F* x * cos(0)

  F = m*a

  
• Energy cannot be created or destroyed

  Change in energy = Work done

  Change = initial energy - Final energy
• Derivation of Potential energy

  Change in energy = F * x * cos(0)

  cos(0) = 1

  Therefore change in energy = m * g * h

  
• Derivation of Kinetic energy:

  Change in energy = F * x * cos(0)

  F = m * a therefore

  Change in energy = m * a * s

  
• Exchange between potential energy to kinetic energy

  M * g * h = 1/2 m * (v)^2

  Mass cancels out

  V ^2 = 2 * g * h

  
• Change in energy = M * g * h - 1/2 * M * V^2

  2 * 9.81 * 5 -1/2 * 2* (8)^2

  = 34.1/7 = 4.9 N


  Calculate resistive force

  
• Power is the rate of work done / rate of energy transfer

  Power = work done/ time

  Power = F * x/time

  Power = Force * speed
• Efficiency = useful output / total output * 100