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Unformatted text preview: Phys 2101 Gabriela Gonzlez There is potential energy associated with the work of conservative forces (gravity: U=mgh; springs: U= kx 2 ): U = U f U i = W If the only forces doing work are conservative the sum of kinetic and potential energy is conserved: U + K = 0 U f + K f = U i + K If there are nonconservative forces, the change in the total energy (potential + kinetic) is equal to the work done by those forces: U + K = W other 2 3 If only conservative forces are in action (gravity, springs, normal forces, tension) then the mechanical energy , the sum of potential and kinetic energy , is conserved. maximum kinetic = minimum potential minimum kinetic = maximum potential 4 In the figure shown, a single frictionless rollercoaster car of mass m tops the first hill with speed v at height h . How much work does the gravitational force do on the car from that point to (a)point A , (b) point B , and (c) point C ? If the gravitational potential energy of the carEarth system is taken to be zero at C , what is its value when the car is at (d) B and (e) A ? (f) If mass m were doubled, would the change in the gravitational potential energy of the system between points A and B increase, decrease, or remain the same? 5 The figure shows a ball with mass m = 0.3 kg attached to the end of a thin rod with length L = 0.5 m and negligible mass. The other end of the rod is pivoted so that the ball can move in a vertical circle....
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 Fall '07
 GROUPTEST
 Physics, Energy, Force, Gravity, Potential Energy, Work

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