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Unformatted text preview: PHYS 211 3/4/09 Chapter 7 Kinetic Energy and Work Constant Forces Variable Force (Spring) Summary Kinetic Energy K = 1 2 mv 2 Work W = K = F d Work transfers energy  sign indicates direction of transfer Force and Work A box is pulled up a rough incline by a rope connected to a pulley. How many forces are doing work on the box? 1) one force 2) two forces 3) three forces 4) four forces 5) no forces are doing work Example (Sample 75) Initially stationary crate of mass m=15.0 kg is pulled, via a cable, a distance d=5.70 m up a frictionless ramp to a height of 2.50 m, where it stops. a) work done by gravitation force Fg? W = F d = mgd cos(90 + ) cos(90 + ) = sin( ) sin( ) = h d W = mgd h d = mgh = (15.0 kg )(9.8 m / s 2 )(2.5 m ) = 368 J b) work done on the crate by Tension T K = W g + W T = W T = W g = 368 J Work and Path Alice and Bill, who happen to have the same mass, both to climb to the top of a mountain. Alice and Bill, who happen to have the same mass, both to climb to the top of a mountain....
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This note was uploaded on 10/03/2011 for the course PHYS 211 taught by Professor Pettie during the Spring '08 term at South Carolina.
 Spring '08
 PETTIE
 Energy, Force, Kinetic Energy, Work

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