A3

• work done 


  the product of the force in the direction of the displacement multiplied by the distance travelled
• work-energy principle


  the net work done on a system is equal to the change in kinetic energy of the system
• total mechanical energy


  the sum of the kinetic energy, gravitational potential energy and elastic potential energy of a body
• kinetic energy


  the energy possessed by a body that is moving
• elastic potential energy


  the energy stored in a body that has been stretched
• gravitational potential energy 


  the work done by a force in moving a body to a positive above its initial position
• power


  the rate at which wok is being done
• efficiency


  the ratio of useful work or power to input work or power
• Conservation of mechanical energy


  the total mechanical energy in a system (i.e., the sum of the potential plus kinetic energies) remains constant as long as the only forces acting are conservative forces
• Conservation of energy

  Energy cannot be created or destroyed, they transfer from one store to another

  the total energy of an isolated system remains constant
• for an isolated system, useful energy + wasted energy outputs = the total energy input
• mechanical energy


  the energy of motion, or the energy of an object that moves
• energy density


  the amount of energy in a fuel per unit volume

  measured in joules per cubic metre (J m–3)
• In the absence of resistive forces, mechanical energy is always conserved.
• When resistive forces (such as friction and drag) are present, mechanical energy is not conserved, and some of it is transferred to the surroundings as thermal energy
• The ‘missing’ mechanical energy is equal to the work done by the resistive forces.
• define work done by a force


  the product of the displacement and the component of the applied force of the object in the direction of displacement
• no motion, no work
• Joules


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  1 Joule = 1 N, 1 m
• work done = change in kinetic energy
• when the change in kinetic energy is positive, work is being done on mass by force
• when the change in kinetic energy is negative, work is done by the resistance
• power = force x velocity
• no change in the acceleration, no work is being done
• constant force = constant acceleration
• constant speed - constant kinetic energy
• Work is the transfer of mechanical energy from one object to another.