1. 1 Everything Science www.everythingscience.co.za 5. Work, energy and power Physics Grade 12

2. 2 Everything Science www.everythingscience.co.za Revision Kinetic energy is the energy an object has due to its motion and can be calculated using: Conservation of Energy: Energy is never created nor destroyed, but is only transformed from one form to another. Conservation of Mechanical Energy: in the absence of non-conservative forces mechanical energy is conserved. EK = 1 2 mv2 3. 3 Everything Science www.everythingscience.co.za Work When a force acting on an object has a component along the line of motion, work is done. Work is the process of transferring energy from object or system to another. W=F x cos Work is done Work is doneWork is not done If more than one force acts at the same time we need to take each force into account when calculating work done. We call the work done after taking all the forces into account the net work done. 4. 4 Everything Science www.everythingscience.co.za Work-energy theorem The work-energy theorem states that the work done on an object by the net force is equal to the change in its kinetic energy: Conservation of energy A conservative force is one for which work done by or against it depends only on the starting and ending points of a motion and not on the path taken. A non-conservative force is one for which work done on the object depends on the path taken by the object. Wnet= Ek=EK ,f EK ,i 5. 5 Everything Science www.everythingscience.co.za Power Power is defined as the rate at which work is done or the rate at which energy is transfered to or from a system. The mathematical definition for power is: Using the definition of work done we can also write this as: And, if F and x are in the same direction we get: P= W t P= F x cos t P=Fv 6. 6 Everything Science www.everythingscience.co.za For more practice see: everythingscience.co.za Shortcode: ESCMK 7. 6 Everything Science www.everythingscience.co.za For more practice see: everythingscience.co.za Shortcode: ESCMK