PHYS171_f11_lecture_28 - How high will it go (neglecting...

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1 PHYS171 Principles of Physics I Chapter 7 Review: Work results in change of potential or kinetic energy { { { { P.E. initial P.E. final P.E. initial 2 P.E. final 2 K.E. initial 2 K.E. final 2 2 2 2 2 i f i f i f x x x mgh mgh kx kx mv mv dx F W f i = = = = 3 2 1 3 2 1 Contrast: When dealing with Newton’s Laws we encountered a force acting for a specified time. Now we deal with force acting over a specified distance . Free particle Spring Gravitational field
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2 Chapter 7 Work results in change of “potential energy” when an object is moved in opposition to an internal force Change in potential energy is independent of the path by which I lift the object F mg movement Calculation of potential energy change is the same for two different paths Chapter 7 Gravitational Potential Energy, Escape Speed r m m G U r r m m G F g g 2 1 12 2 2 1 ˆ = = r 1 m 2 m
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3 Chapter 7 Example problem At the earth’s surface a projectile is launched straight up at 10 km/s.
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Unformatted text preview: How high will it go (neglecting air resistance and earth rotation). How high would we calculate if we assumed constant acceleration of gravity? Chapter 7 Outcome of Work The outcome of work is to change the energy of the object If we do no work on the system, there will be no change in energy, but this does not exclude the possibility that kinetic energy is converted to potential energy, or visa versa. If an internal force does work it results in a transfer of energy from one form to another. If some external force does work on the system or if there is a nonconservative force (i.e., friction) the total energy of the system will change...
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PHYS171_f11_lecture_28 - How high will it go (neglecting...

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