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Work and Energy mechanical work mechanical energy Work The amount of work depends on: 1. The force you have to exert 2. The distance moved in the direction of the force Work done by a force = (joule, J) force x distance moved in direction of force = (newton, N) x (metre, m) Example: Since both force and displacement are in the same direction, this would give a work of 20 Joules. W = 10 N x 2 m = 20J Work and Energy Amount of work done = amount of energy transferred Changing their gravitational potential energy Changing their kinetic energy Changing their gravitational potential energy Gravitational potential energy is energy stored within a physical system as a result of the height on Earth surface. Ep = m · g · h work done by a force = gravitational potential energy = Ep = force x distance moved in direction of force weight x m·g ·h vertical height difference Changing their kinetic energy Ec 1 m v2 2 The kinetic energy of an object is the energy which it possesses due to its motion. work done by a force = force 1 kinetic energy mass speed 2 2 x distance moved in direction of force 1 Ec m v 2 2 Example: If vo = 0 m/s and its mass is 4 kg then the trolley has a final velocity of 1 Ec m v 2 2 30 1 4 v2 2 v2 30 15 2 v 3,87 m s Example: mechanical energy and law of conservation of energy Mechanical energy describes the sum of potential energy and kinetic energy present in the components of a mechanical system. E m = Ec + Ep The law of conservation of energy is an empirical law of physics. It states that the total amount of energy in an isolated system remains constant over time. In mechanics, conservation of energy is usually stated as Em1 = Em2 Ec1 + Ep1 = Ec2 + Ep2 Example: Example: Example: Example: