12/4/13 Objective: Determine the power required to do a given amount of work Question: If I do 20 J of work in 5 seconds and you do 20 J of work in 10 seconds, who uses more power? Work Remember from yesterday: Work is done when we apply a force over a distance: W = Fd Work equals the force exerted on an object in the direction of motion, times the objects displacement F = 20 N d= 5 m W = (20 N)(5 m) = 100 J Power In physics, power is defined as work done per unit of time P = W/t We measure power in Watts. 1 W = 1 J/1 s If I do 20 J of work in 5 seconds, I use 4 W of power. Power Since P = W/t, doing more work is one way to increase the amount of power Doing work more quickly also increases the amount of power used. Power practice problems P. 264, #9-13 When you finish, grab a yellow worksheet and start working on that Youll be handing in both the book problems and yellow sheet tomorrow