Unformatted text preview: 6.30. IDENTIFY: The magnitude of the work can be found by finding the area under the graph. SET UP: The area under each triangle is 1/2 base height . x F , so the work done is positive when x increases during the displacement. EXECUTE: (a) 1/ 2 (8 m)(10 N) 40 J . (b) 1/ 2 (4 m)(10 N) 20 J . (c) 1/ 2 (12 m)(10 N) 60 J . EVALUATE: The sum of the answers to parts (a) and (b) equals the answer to part (c). 6.42. IDENTIFY: Apply tot 2 1 W K K to the brick. Work is done by the spring force and by gravity. SET UP: At the maximum height. v . Gravity does negative work, grav W mgh . The work done by the spring is 2 1 2 kd , where d is the distance the spring is compressed initially. EXECUTE: The initial and final kinetic energies of the brick are both zero, so the net work done on the brick by the spring and gravity is zero, so 2 (1 2) kd mgh , or 2 2 / 2(1.80 kg)(9.80 m /s )(3.6 m)/(450 N / m) 0.53 m. d mgh k The spring will provide an upward force while the spring and the brick are in contact. When this force goes to zero, the spring is at its uncompressed while the spring and the brick are in contact....
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This note was uploaded on 04/03/2008 for the course PHYSICS 140 taught by Professor Evrard during the Fall '07 term at University of Michigan.
 Fall '07
 Evrard
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