Lecture-Example (posted before lecture) 9/23 (Friday) Example 4-18 (page 95): A 30 kg box is pulled by a rope moving along a horizontal floor. The rope is 30 above the horizontal, and the pulling force is 100 N. (a) What is the normal force acting on the box from the floor? (b) If uk is 0.25, what is the acceleration? Example: John holds a string. An object is attached to the other end of the string. John starts swinging the object in a horizontal circle. What is the source of the centripetal force? Exercise C a e 114 : A rider on a Ferris wheel moves in a vertical circle of radius r at constant speed v. Is the normal force that the seat exerts on the rider at the top of the wheel (a) less than, (b) more than, (c) the same as, the normal force the seat exerts at the bottom of the wheel? Example 5-6: What is the maximum speed with which a 1500 kg car can make a turn around a curve of radius 20 m on the unbanked (flat) road without sliding? What is the source of the centripetal force? Example 5-7: A curve on a racetrack of radius 70 m is banked at a 15 angle. At what speed can a car take this curve without assistance from friction? Example: When someone swings a bucket of water in a vertical circle, the water will not fall off on the top of the circle if the speed is fast enough. Question: how fast