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lecture5 - Phys 2101 Gabriela González 2 Work-energy...

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Unformatted text preview: Phys 2101 Gabriela González 2 Work-energy theorem : The change in kinetic energy of a particle is equal to the net work done on the particle by all external forces. W = F • d x a b ∫ = Δ KE = 1 2 mv a 2 − 1 2 mv b 2 Consider a constant 1-D force producing constant acceleration a, starting from rest. In time t, the work done by the force is Fd, where d is the distance traveled, ½ a t 2 . At time t, the velocity is v=at, so the kinetic energy is K = ½ mv 2 = ½ m(at) 2 = (ma) ( ½ a t 2 ) = Fd 3 A variable force F acts along the x-axis on a 10kg mass. The particle starts moving to the right with speed 2 m/s at x=0. a) Describe the motion of the mass. b) At what position does the particle has maximum and minimum kinetic energy? c) Plot the position versus time for the particle. d) What is the expression for the force as a function of position? -2 F(N) x(m) -1 0 1 2 10 20 -10 3 A variable force F acts along the x-axis on a 10kg mass. The particle starts moving to the right with speed 2 m/s at x=0. a) Describe the motion of the mass. b) At what position does the particle has maximum and minimum kinetic energy? c) Plot the position versus time for the particle. d) What is the expression for the force as a function of position? -2 F(N) x(m) -1 0 1 2 10 20 -10 -20 4 Hooke’s law: Key concepts: • d: displacement from free, relaxed end •-ve sign: “restoring” force • large k: “stiff”, small k= “soft” In one dimension, with the origin at the free, relaxed end: F = ¡ k x d k F − = 5...
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This note was uploaded on 12/01/2011 for the course PHYS 2101 taught by Professor Grouptest during the Fall '07 term at LSU.

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lecture5 - Phys 2101 Gabriela González 2 Work-energy...

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