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Announcements

Announcements. Homework for tomorrow… (Ch. 9, Prob 26, 33, & 34) 9.8: ΔK = mv 2 /6 9.16: a) 0.12 m b ) 0.36 J c ) -0.36 J d ) 0.06 m e)9 x 10 -2 J 9.18: 25 J Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm

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Announcements

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  1. Announcements • Homework for tomorrow… (Ch. 9, Prob 26, 33, & 34) 9.8: ΔK = mv2/6 9.16: a) 0.12 mb) 0.36 J c) -0.36 J d) 0.06 m e)9 x 10-2 J 9.18: 25 J • Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm • Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm T 8 am-7 pm F 8 am-5 pm

  2. Chapter 9 Kinetic Energy & Work (Work in more than 1D & the Dot Product)

  3. Review… • Work done by a constant force (in more than 1D) • Net Work-Kinetic Energy Theorem • The work done by a force is equal to the area under a force vs position graph

  4. Example A sledge loaded with bricks has a total mass of 18.0 kg and is pulled at constant speed by a rope inclined at 20.0º above the horizontal. The sledge moves a distance of 20.0 m on a horizontal surface. The coefficient of kinetic friction between the sledge and surface is 0.500. • What is the tension in the rope? • How much work is done by the rope on the sledge? • What is the work done by friction?

  5. Section 9.8: Multiplying a Vector by a Vector: The Dot Product The scalar or dot product is defined as… which can be written as

  6. Work done by a Constant Force The work done by a force on a particle (in more than 1D)? in terms of the dot product

  7. Work done by a Variable Force The work by a force on a particle (in more than 1D)? where

  8. Work done by a Variable Force (in 3D) The work W done by a force while the particle moves from (x1, y1, z1) to (x2, y2, z2) is given by: where

  9. Example Starting from rest, a 5.00-kg block slides 2.50 m down a rough 30.0° incline. The coefficient of kinetic friction between the block and the incline is kin= 0.436. Determine • the work done by the force of gravity • the work done by the friction force between the block and incline, and • the work done by the normal force. • the total work done on the block. • the speed of the block at 2.50 m

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