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Unformatted text preview: P112 Spring 2007 Homework #7 Due: Friday March 9th, 2007 – At lecture Reading: 5.5, 6.16.3, 7.1 Not all concepts will be covered in class – you are responsible for all material in the reading and in the homework problems. Warmup Exercises: (Answer only will be marked) 1. A force of 800 N stretches a certain spring a distance of 0.200 m. a) What is the potential energy of the spring when it is stretched 0.200 m? b) What is its potential energy when it is compressed 5.00 cm? 2. A 4.80kg watermelon is dropped from rest from the roof of a 25.0mtall building. a) Calculate the work done by gravity on the watermelon during its displacement from the roof to the ground. b) What is the kinetic energy and the speed just before it strikes the ground? Mathematics Exercises: 3 . A twodimensional function U is given in terms of x and y coordinates by U(x,y)= ½ k (x 2 +y 2 ), where k is a constant. The vector F is given by the “gradient” of U: r F = " r # U . What is the magnitude of the vector F at any point? Show your work. Estimation: (Marked based solely on logic) 4. According to some recent highly accurate measurements made from satellites, the continent of North America is drifting at a rate of about 1 cm per year. Assuming a continent is about 50 km thick, estimate the kinetic energy the continental US has as a result of this motion....
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This note was uploaded on 03/27/2008 for the course PHYS 1112 taught by Professor Leclair,a during the Spring '07 term at Cornell.
 Spring '07
 LECLAIR,A
 mechanics, Work

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