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Lecture 15

Lecture 15. Wednesday, October 1 More Newton’s Laws. Estimated number of Juveniles the US has detained as enemy combatants since 2002. 2,500. Quiz. An elevator, lifted by a cable, is going up at a steady speed. Identify the forces acting on the elevator. Make a free body diagram.

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Lecture 15

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  1. Lecture 15 Wednesday, October 1 More Newton’s Laws

  2. Estimated number of Juveniles the US has detained as enemy combatants since 2002 • 2,500

  3. Quiz • An elevator, lifted by a cable, is going up at a steady speed. • Identify the forces acting on the elevator. Make a free body diagram. • Is T greater than, equal to, or less than w? Or is there not enough information to tell? Slide 4-23

  4. Homework questions?

  5. Monday Review • Equilibrium FNET = 0 • Frictional forces

  6. Today • Sections 5:6-8 • 5.6 Drag, read but I will not hold you responsible. Skip problems 5:30, 31 • 5.7 Interacting objects– applications of Newton’s Third Law • 5.8 Ropes and Pulleys—tension—work example like last week’s lab

  7. Review Example Macie pulls a 40 kg rolling trunk by a strap angled at 30° from the horizontal. She pulls with a force of 40 N, and there is a 30 N rolling friction force acting on trunk. What is the trunk’s acceleration? Slide 5-17

  8. The coefficient of static friction is • 1. smaller than the coefficient of kinetic friction. • 2. equal to the coefficient of kinetic friction. • 3. larger than the coefficient of kinetic friction. • 4. not discussed in this chapter.

  9. Problem • 5:24 A 23kg child on slide inclined at 380. • What forces act on child? • Make a free body diagram • Magnitude of normal force? • If the coefficient of static friction is 0.62, will the child start to slide?

  10. Problem, interacting bodies Glider on a air track Massless, frictionless pulley m1 m2

  11. Problem MC26Dog in an elevator

  12. Problem MC30Two blocks on an inclined plane

  13. Problems due Friday • 5:24, 25, 29, 30, 31, 35, 36, 37, 39 • Special assignment to be handed in Friday: Workbook pages 4-5 and 4-6, exercises 17-22 and page 5-5, exercises 13-15.

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