19-kinetic energy and work 2

19-kinetic energy and work 2 - PHYS 211 3/4/09 Chapter 7...

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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 7-5) 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.

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19-kinetic energy and work 2 - PHYS 211 3/4/09 Chapter 7...

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