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UNIT 4 Work, Energy, and Power

UNIT 4 Work, Energy, and Power. ConcepTest 6.2a Friction and Work I. 1) friction does no work at all 2) friction does negative work 3) friction does positive work. A box is being pulled across a rough floor at a constant speed. What can you say about the work done by friction?.

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UNIT 4 Work, Energy, and Power

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  1. UNIT 4Work, Energy, and Power

  2. ConcepTest 6.2aFriction and Work I 1) friction does no work at all 2) friction does negative work 3) friction does positive work A box is being pulled across a rough floor at a constant speed. What can you say about the work done by friction?

  3. displacement N Pull f mg ConcepTest 6.2aFriction and Work I 1) friction does no work at all 2) friction does negative work 3) friction does positive work A box is being pulled across a rough floor at a constant speed. What can you say about the work done by friction? Friction acts in the opposite direction to the displacement, so the work is negative. Or using the definition of work: W = F d cos q since = 180o, thenW < 0

  4. Monday November 7th Introduction to WORK

  5. TODAY’S AGENDA Monday, November 7 • Intro to Work • Mini-Review: Lab 4 Calculation Discussion • Mini-Lesson: Properties of Work • Hw: Practice A (All) p162 UPCOMING… • Tue: Types of Energy • Wed: Work-KE Theorem • Thur: Potential Energy

  6. Work The work done by a constant force is defined as the distance moved multiplied by the component of the force in the direction of displacement: Energy

  7. Work What is the correct unit of work expressed in SI units? (A) kg m2/s2 (B) kg m2/s (C) kg m/s2 (D) kg2 m/s2

  8. Work How much work did the movers do (horizontally) pushing a 160 kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50?

  9. Work Can work be done on a system if there is no motion? (A) Yes, if an outside force is provided. (B) Yes, since motion is only relative. (C) No, since a system which is not moving has no energy. (D) No, because of the way work is defined.

  10. END

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