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Unformatted text preview: PHYS 218  SOLUTION TO ASSIGNMENT 1 02 Feb 2007 By Eliot Kapit and Chung Koo Kim email : ek359@cornell.edu and ck269@cornell.edu 1. Damped Harmonic Motion (a) Quite obviously, this is a damped pendulum; the factor of exp . 25 t indicates that the oscillation will decay with time. (b) See graph: (c) We can extract the damping, = 2 * . 25 = 0 . 5 s 1 , the oscillation frequency b = 12 s 1 , the natural frequency = p b 2 + 2 / 4 = 37 . 7 s 1 and the initial phase shift = 3. One cannot measure the mass since the acceleration from gravity is independent of it, and terms such as and F all depend on the existence of a driving force, which is not present in this problem. (d) T = 2 / = 1 / 6. The other characteristic time is the decay constant = 1 / . 25 = 4 s , which is the time it would take for the amplitude to decay by a factor of 1 /e . 2. Effect of gravity on a hanging spring (a) One arrow pointing down, and another one up, representing weight (= mg ) and restoring force of spring ( = k ( l l )), respectively. (Diagram omitted) (b) From Newtons 2nd law for vertical direction, mg k ( l l ) = 0, or l = l + mg k 1 (c) If the mass is pulled down by y from the new equilibrium, we get, from...
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 Spring '08
 PETERWITTICH

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