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Unformatted text preview: Ph 111.01 November 10, 2008 PS 11a (28) Problem 1. The height of a tower is measured by attaching a simple pendulum to its ceiling, whose length is barely enough to stay off the floor. The pendulum is let go from a small angle, and takes 12 s to return to the same location it started from. a.) How tall is the tower? m If the pendulum mass is let go 0.2 m above the floor, b.) how fast is the mass traveling as it grazes the floor? m/s Solution. (a) The period of the pendulum is related to the length of the pendulum, H in this case, by 2 H T g = . So, the height must be ( ) ( ) 2 2 2 2 2 2 9.8 m/s 12 s 35.8 m 4 4 H T g gT H = = = = (b) This is a matter of conservation of energy. The potential energy when it is released is converted into kinetic energy at the bottom of its motion. 2 1 2 mgh mv = giving ( ) ( ) 2 2 2 9.8 m/s 0.2 m 1.980 m/s v g h = = = Problem 2. An astronaut on a small planet wishes to measure the local value of g by timing pulses traveling down a wire which has a large mass suspended from it. Assume that the wire has a mass of traveling down a wire which has a large mass suspended from it....
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 Fall '08
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