Chapter07

# Chapter07 - Chapter 7: Potential Energy and Energy...

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Chapter 7: Potential Energy  and Energy Conservation

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1. Gravitational Potential Energy Gravity does _______ work on mass. potential energy __________ Gravity does _______ work on mass. potential energy __________
Work done by gravity Gravitational potential energy Then, 2 1 1 2 ˆˆ ( ) (( ) ) gravity W F s mgj y y j mgy mgy = = - - = - r r U mgy = 1 2 2 1 ( ) gravity W U U U U U = - = - - = -∆

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Conservation of Mechanical Energy For gravitational force 2 1 2 1 ( ) gravity tot W W K K U U = = - = - - 1 1 2 2 K U K U + = + constant E K U = + = Conservation of Mechanical Energy 2 1 2 E K U mv mgy = + = +
Since and , the potential energy is r ref is the position where the potential energy is zero For gravitational force at the Earth’s surface W U = -∆ W F dr = r r ref r r U F dr = - r r 0 ( ) y U mg dy mgy = - - =

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Example 7.1) You throw a 0.145 kg baseball straight up in the air, giving it an initial upward velocity of magnitude 20.0 m/s. Find how high it goes.
Example 7.4) A skater moves through a quarter-circle with radius R=3.00 m. The mass of the skater and his skateboard is 25.0 kg. Find a) his speed at the bottom of the ramp b) the normal force that acts on him at the bottom of the curve

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2. Elastic Potential Energy
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## This note was uploaded on 02/13/2012 for the course RANDOM 100 taught by Professor Idk during the Fall '08 term at Virginia Tech.

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Chapter07 - Chapter 7: Potential Energy and Energy...

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