Lecture 15 Wednesday, October 1 More Newton’s Laws

Estimated number of Juveniles the US has detained as enemy combatants since ,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. Is T greater than, equal to, or less than w? Or is there not enough information to tell? Slide 4-23

Homework questions?

Monday Review Equilibrium F NET = 0 Frictional forces

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

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

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.

Problem 5:24 A 23kg child on slide inclined at 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?

Problem, interacting bodies Glider on a air track Massless, frictionless pulley m1m1 m2m2

Problem MC26 Dog in an elevator

Problem MC30 Two blocks on an inclined plane

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 and page 5-5, exercises