Key Areas covered Work done potential energy kinetic

Key Areas covered • Work done, potential energy, kinetic energy and power in familiar and unfamiliar situations. • Conservation of energy

What we will do today • Revise conservation of energy from N 5. • State the law of conservation of energy. • Carry out calculations of the conservation of energy using formulae for work done, potential energy and kinetic energy as well as power.

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Conservation of Energy

The total energy of any closed system is conserved, although energy may change its form. E. g. energy ‘lost’ as it changes to heat, light, sound, etc. Ep = mgh Ek = ½mv² Work Done = Force x Displacement Ew = Fd Energy and Work are measured in Joules (J).

Combining Ep and Ek to find v • Using the conservation of energy, we can combine the equations for Ep and Ek to find a value for velocity, v, without needing to know the mass: Ep = Ek mgh = ½ mv 2 gh = ½v 2 v = √ 2 gh

Power is the rate of transformation of energy from one form to another. P = = energy / time work done / time (F x displacement) / time F x average velocity Power is measured in Watts (W).

2003 Qu: 4

2008 Qu: 4

2006 Qu: 21

Open-ended question • Some cars are fitted with a system that stores the energy normally lost as heat in the brakes. Estimate the maximum energy that could be stored as a car is decelerated to rest. Clearly show any estimates you make in your calculation and show your working. 3 marks

Example answer 1

Example answer 2