Chapter 5 Pgs. 167-192
OBJECTIVES Relate the concepts of energy, time, and power. Calculate power in two different ways.
Power The rate at which work is done The rate of energy transfer Three variations of the equation: W Fd P = ----- P = ----- P = Fv ∆t ∆t
Power SI unit for power is the watt (W) Named after James Watt who perfected the steam engine. Horsepower (hp) is also used 1 hp = 746 W Machines with different power ratings will do the same amount of work in different time intervals
A 193 kg curtain needs to be raised 7 A 193 kg curtain needs to be raised 7.5 m, at a constant speed, in as close to 5.0 s as possible. The power ratings for three motors are listed as 1.0 kW, 3.5 kW, and 5.5 kW. Which machine is the best for the job?