1. Work and Energy October 17, 2005

2. Your instructor releases a bowling ball as demonstrated. The ball will 60 0 of 5 1.Return to its original release height. 2.Rise to some decreased height. 3.Rise to a higher height. 4.Depends on the speed of the ball at release. 1, 2 and 4 are correct depending on assumptions. If initial velocity

3. A box is being pulled across a rough floor at a constant speed. What can you say about the work done by friction? 60 0 of 5 1.Friction does no work at all. 2.Friction does negative work. 3.Friction does positive work.

4. A ball tied to a string is being whirled around in a circle. What can you say about the work? 90 0 of 5 1.The tension does no work at all. 2.The tension does positive work. 3.The tension does negative work.

5. You lift a book with your hand in such a way that it moves up at constant speed. While it is moving, what is the total work done on the book? 90 0 of 5 mg rrrr F HAND v = const a = 0 1.mg   r 2.F HAND   r 3.(F HAND + mg)   r 4.zero 5.none of the above

6. Answers 1.1, 2 and 4 are correct depending on assumptions. If initial velocity is zero and no air resistance, then 1. If initial velocity is zero and air resistance, then. An initial velocity affects resulting height so 4 could also be right. 2.2 - negative work 3.1 - no work 4.4 - zero