Concept #1: Work Done by a Constant Force
Practice: You pull a 5-kg object vertically up with a constant 100-N for 2 m. How much work do you do?
Example #1: Work by a Constant Force
Practice: A water skier is pulled by a boat (shown). Both move north with a constant 10 m/s. The tension on the rope is 150 N, and makes an angle of 53° with the horizontal. How much work is done by the rope in 5 seconds?
Concept #2: Zero Work, Negative Work & Work by Friction
Practice: A 3-kg box sits on a level surface. The box-surface coefficient of friction is 0.4. You pull on the box with 20 N at 37o above the horizontal for 5 meters. Calculate the work done by:
(c) weight; and
How much energy was dissipated? Where did this energy “go” ?