# Physics, P2.2

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• Created by: KatyN
• Created on: 13-11-14 17:45
• P2.2.1 Forces and Energy
• A) When a forces causes an object to move through a distance work is done
• Whenever something moves somethign else it is providing some sort of effort to move it.
• The thing putting in the effort needs a supply of energy (normally in the form of food or fuel)
• It then does work by moving the object- and one way or another it transfers the energy it receives into other forms
• Whether this energy is transferred usefully or it is wasted, you can still say that energy has been transferred and work is done. Work done and energy transferred are one and the same, and both given in joules.
• B) Work done, force and distance are related by the equation:    W = F x D
• [W is the work done in joules, F is the force applied in Newtons and D is the distance moved in the direction of the force in metres.]
• C) Energy is tranfserred when work is done
• Whether this energy is transferred usefully or it is wasted, you can still say that energy has been transferred and work is done. Work done and energy transferred are one and the same, and both given in joules.
• D)Work done against frictional forces
• E) Power is the work done or energy transferred in a given time.            P= E/T
• Power is not the same thing as force, nor energy. A powerful machine is not necessarily one which can exert a strong force
• A powerful machine is one which transfers a lot of energy in a short space of time
• The proper unit of power is the Watt., One watt is equal to one joule of energy transferred per second. Power means how much energy per second is being transferred.
• There are a few ways of calculating the power output of a person:
• A) the timed run upstairs- in this case the energy transferred is the potential energy you gain. so power= mxgxh/t
• F) Gravitational Potential energy is the energy that an object has by virtue of its position in a gravitational field
• Gravitational Potential energy is the energy that an object has because of its vertical position in a gravitational field
• When an object is raised vertically, work is done against the force of gravity and the object gains gravitational potential energy.
• On Earth, the gravitational field strength is around 10N/Kg, unless specified differently in an exam question, use this
• B) the timed acceleration- This time the energy transferred is the kinetic energy you gain. So power= 1/2xmxv^2/t
• G) The kinetic Energy of an object depends on its mass and its speed:        E(k)= 1/2 x m x v^2
• The more an object weighs and the faster it is going, the bigger its kinetic energy will be.
• when something falls, its potential energy is converted into kinetic energy, so the further it falls the faster it gets.
• some of the gravitational potential is transferred into heat and sound energy, which is why meteors that hit earth burn up
• F) Gravitational Potential energy is the energy that an object has by virtue of its position in a gravitational field
• Gravitational Potential energy is the energy that an object has because of its vertical position in a gravitational field
• When an object is raised vertically, work is done against the force of gravity and the object gains gravitational potential energy.
• On Earth, the gravitational field strength is around 10N/Kg, unless specified differently in an exam question, use this
• G) The kinetic Energy of an object depends on its mass and its speed:        E(k)= 1/2 x m x v^2
• The more an object weighs and the faster it is going, the bigger its kinetic energy will be.
• when something falls, its potential energy is converted into kinetic energy, so the further it falls the faster it gets.
• some of the gravitational potential is transferred into heat and sound energy, which is why meteors that hit earth burn up