# Work, Energy and Momentum

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• Work, Energy and Momentum
• Energy and Work
• When work is done, the supplied energy is transferred to the object so the work done is equal to the energy transferred
• W=F X D
• Work done s measured in Joules
• The work done to overcome friction is transferred into energy by heating
• Gravitational Potential Energy
• Energy stored in an object due to its position on Earth's gravitational field
• Ep=m x g x h
• Power is the rate of transfer energy
• P= E/T
• Power- Watts (W)
• Kinetic Energy
• The greater the mass the faster the speed of the object- the more kinetic energy it has
• Energy in elastic once being stretched is called Elastic Potential Energy
• When the elastic returns to its original shape the energy is released
• Momentum
• All moving objects have momentum
• The greater the mass the greater velocity of an object- the greater its momentum
• p= m x v
• Law of conservation of Momentum
• The total change in momentum is zero
• The total momentum before is equal to the total momentum after
• Explosions
• In and explosion the objects move apart with equal and opposite momentum
• One direction must be defined as positive and the opposite must be defined negative
• So the total momentum after the explosion is zero
• Impact forces
• When a force acts on a moving object, its momentum changes
• The longer the time taken for change in momentum, the smaller the force then acts
• If the impact time is short, the force is large. As impact time increases the forces become less
• Crumple zones- e.g. cars folding in on themselves increases the impact time so reduces the force on the car