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Potential and Kinetic Energy
Chapter 8.3 – 8.6
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Energy Something that enables an object to do work Mechanical energy
The energy due to the position of something or the movement of something Two types: Potential & Kinetic Energy
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Potential Energy Energy that is stored and held in readiness Examples:
Has the potential for doing work Examples: Stretch or compress spring Chemical energy in fuel
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Potential energy = mgh = mass * gravity acceleration * height
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Practice problem: If the biker has a mass of 50 kg and the hill is 100 m high. What is the biker’s potential energy? PE=mgh= 50* 10*100 50,000 J
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Practice problem: If you pick up a 100 N boulder 2 meters in the air, how much potential energy does the boulder have? Work against gravity = potential energy W=Fd=PE 100*2= 200 J
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Practice Problem: How much potential energy does a 100 N boulder gain if you carry it horizontally across a 10-m room? None, you do not do work on the boulder moved horizontally, because you apply no force to the boulder. Therefore, it does not gain any potential energy.
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Kinetic Energy Energy of motion KE = ½mv2
Kinetic energy of a moving object is equal to the work required to bring it to that speed from rest
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Practice Problem: If the speed of an object is squared, how does this impact the object’s kinetic energy? KE= ½mv2 It is quadrupled
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Law of Conservation of Energy
Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.
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What is the PE of a 10 kg cart at A?
What is the KE of a 10 kg cart at A? What is the ME of a 10 kg cart at A?
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What is the PE at bottom of hill between A & B?
What is the KE at bottom of hill between A & B? What is the ME at bottom of hill between A & B? What is the speed of a 10 kg cart at this spot?
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What is the PE at B? What is the KE at B? What is the ME at B?
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What is the PE at C? What is the KE at C? What is the ME at C? What is the speed of the cart at C?
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How long does it take to travel from point C to D?
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