1. PHY 2048C General Physics I with lab Spring 2011 CRNs 11154, 11161 & 11165 Dr. Derrick Boucher Assoc. Prof. of Physics Sessions 6-7, Chapter 7

2. Chapter 6. Clicker Questions

3. A Martian lander is approaching the surface. It is slowing its descent by firing its rocket motor. Which is the correct free-body diagram for the lander?

4. An elevator that has descended from the 50th floor is coming to a halt at the 1st floor. As it does, your apparent weight is A. less than your true weight. B. equal to your true weight. C. more than your true weight. D. zero.

5. The terminal speed of a Styrofoam ball is 15 m/s. Suppose a Styrofoam ball is shot straight down with an initial speed of 30 m/s. Which velocity graph is correct?

6. Topics: Interacting Objects Analyzing Interacting Objects Newton’s Third Law Ropes and Pulleys Examples of Interacting-Object Problems Chapter 7. Newton’s Third Law

7. Interacting Objects If object A exerts a force on object B, then object B exerts a force on object A. The pair of forces, as shown, is called an action/reaction pair.

11. EXAMPLE 7.3 The forces on accelerating boxes

15. Example, Problem 7-30, p. 206

16. Example, Problem 7-32, p. 207

17. Chapter 7. Summary Slides

18. General Principles

20. Important Concepts

22. Applications

24. Chapter 7. Clicker Questions

25. Car B is stopped for a red light. Car A, which has the same mass as car B, doesn’t see the red light and runs into the back of B. Which of the following statements is true? A. A exerts a larger force on B than B exerts on A. B. A exerts a force on B but B doesn’t exert a force on A. C. B exerts a force on A but A doesn’t exert a force on B. D. B exerts a larger force on A than A exerts on B. E. B exerts the same amount of force on A as A exerts on B.

26. Boxes A and B are sliding to the right across a frictionless table. The hand H is slowing them down. The mass of A is larger than the mass of B. Rank in order, from largest to smallest, the horizontal forces on A, B, and H. A. F H on B = F H on A > F A on B B. F B on H = F H on B = F A on B = F B on A C. F B on H = F H on B < F A on B = F B on A D. F B on H = F H on B > F A on B = F B on A

27. A. Equal to B. Greater than C. Less than All three 50 kg blocks are at rest. Is the tension in rope 2 greater than, less than, or equal to the tension in rope 1?

28. In the figure to the right, is the tension in the string greater than, less than, or equal to the weight of block B? Assume that the system is free to move. A. Equal to B. Greater than C. Less than

29. A small car is pushing a larger truck that has a dead battery. The mass of the truck is larger than the mass of the car. Which of the following statements is true? A.The truck exerts a larger force on the car than the car exerts on the truck. B.The truck exerts a force on the car but the car doesn’t exert a force on the truck. C.The car exerts a force on the truck but the truck doesn’t exert a force on the car. D.The car exerts a larger force on the truck than the truck exerts on the car. E.The car exerts the same amount of force on the truck as the truck exerts on the car.

30. The propulsion force on a car is due to A. static friction. B. kinetic friction. C. the car engine. D. elastic energy.

31. Is the tension in rope 2 greater than, less than, or equal to the tension in rope 1? A. greater than rope 1 B. less than rope 1 C. equal to rope 1

32. Chapters 7 Practice Problems Chap 7: 21, 27, 31, 33, 35, 41 Unless otherwise indicated, all practice material is from the “Exercises and Problems” section at the end of the chapter. (Not “Questions.”)