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Work and Elastic Potential Energy

Work and Elastic Potential Energy. Work. Applying a force over a distance. W = F  ∆x The force can’t be zero. The distance can’t be zero. Three Cases. Force Parallel to Motion Speeds it up Increases Energy Positive work Force Anti-Parallel to Motion Slows it down

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Work and Elastic Potential Energy

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  1. Work and Elastic Potential Energy

  2. Work • Applying a force over a distance. • W = F∆x The force can’t be zero. The distance can’t be zero.

  3. Three Cases • Force Parallel to Motion • Speeds it up • Increases Energy • Positive work • Force Anti-Parallel to Motion • Slows it down • Decreases Kinetic Energy – Negative work • Force Perpendicular to Motion • Neither slows it down nor speeds it up. • Doesn’t change Kinetic Energy • Zero Work

  4. Work of a Spring • F = k∆x • W = F∆x • What is the force?

  5. Work of a Spring Work = Fave∆x = ½ k∆x*∆x = ½ kx2

  6. Fundamental Theorem • ΣW = ∆K • The sum of all work equals the change in Kinetic Energy. • Review HW Problems • Check in: A car of mass 1000 kg goes from a speed of 10 m/s to a speed of 20 m/s. How much work was done on the car? • 150,000 J

  7. Work and Potential Energy • Work you do against gravity or against a spring is not lost but stored as potential energy. • The amount of work you do is the amount of energy stored. • For gravity your work is F*∆x = mg∆h • What is the effect of the direction of the force compared to the direction of the motion? • For a spring, your work is ½ kx2 • Us = ½ kx2 • Try problem 5 and 6 from the energy conservation worksheet.

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