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UNIT 4 Work, Energy, and Power

UNIT 4 Work, Energy, and Power. ConcepTest 6.3 Force and Work. 1) one force 2) two forces 3) three forces 4) four forces 5) no forces are doing work. A box is being pulled up a rough incline by a rope connected to a pulley. How many forces are doing work on the box?. displacement.

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UNIT 4 Work, Energy, and Power

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  1. UNIT 4Work, Energy, and Power

  2. ConcepTest 6.3Force and Work 1) one force 2) two forces 3) three forces 4) four forces 5) no forces are doing work A box is being pulled up a rough incline by a rope connected to a pulley. How many forces are doing work on the box?

  3. displacement N T f mg ConcepTest 6.3Force and Work 1) one force 2) two forces 3) three forces 4) four forces 5) no forces are doing work A box is being pulled up a rough incline by a rope connected to a pulley. How many forces are doing work on the box? Any force not perpendicularto the motion will do work: N does no work T does positive work f does negative work mg does negative work

  4. Tuesday November 8th KINETIC ENERGY

  5. TODAY’S AGENDA Tuesday, November 8 • Kinetic Energy • Hw: Practice B (All) p165 UPCOMING… • Wed: Potential Energy • Thur: Conservation of Mechanical Energy

  6. Section 2 Energy Chapter 5 Kinetic Energy • Kinetic Energy The energy of an object that is due to the object’s motion is called kinetic energy. • Kinetic energy depends on speed and mass.

  7. Section 2 Energy Chapter 5 Kinetic Energy, continued • Work-Kinetic Energy Theorem • The net work done by all the forces acting on an object is equal to the change in the object’s kinetic energy. • The net work done on a body equals its change in kinetic energy. Wnet= ∆KE net work = change in kinetic energy

  8. Section 2 Energy Chapter 5 Sample Problem Work-Kinetic Energy Theorem On a frozen pond, a person kicks a 10.0 kg sled, giving it an initial speed of 2.2 m/s. How far does the sled move if the coefficient of kinetic friction between the sled and the ice is 0.10?

  9. Section 2 Energy Chapter 5 Sample Problem, continued Work-Kinetic Energy Theorem 1. Define Given: m = 10.0 kg vi = 2.2 m/s vf = 0 m/s µk = 0.10 Unknown: d = ?

  10. Section 2 Energy Chapter 5 Sample Problem, continued Work-Kinetic Energy Theorem 2. Plan Choose an equation or situation: This problem can be solved using the definition of work and the work-kinetic energy theorem. Wnet = Fnetdcosq The net work done on the sled is provided by the force of kinetic friction. Wnet = Fkdcosq = µkmgdcosq

  11. Section 2 Energy Chapter 5 Sample Problem, continued Work-Kinetic Energy Theorem 2. Plan, continued The force of kinetic friction is in the direction opposite d, q = 180°. Because the sled comes to rest, the final kinetic energy is zero. Wnet = ∆KE = KEf - KEi = –(1/2)mvi2 Use the work-kinetic energy theorem, and solve for d.

  12. Section 2 Energy Chapter 5 Sample Problem, continued Work-Kinetic Energy Theorem 3. Calculate Substitute values into the equation:

  13. END

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