Power Power Defined Power The rate at which

Power

Power Defined • Power: The rate at which energy is transferred or transformed – The rate at which work is done

Units of Power • Since the units are: Joule/second or J/s • J/s is equivalent to a watt – Named after James Watt – Credited with making improvements on the first steam engine

Horsepower • Horsepower – Watt conducted an experiment where a horse could do 33, 000 foot-pounds of work a minute in drawing coal from a coal pit. – foot-pound is the work done when a weight (force) of 1 lb is moved through a distance of 1 ft.

Horsepower(continued) – Watt estimated that a horse can do 550 ft-lb of work per sec, which is equivalent to 746 watts. – 1 horsepower(H. P. ) = 746 watts

Alternate Calculation • Since but, • therefore

Power problem #1 • How long does it take to raise a 250 kg garage door 3 m with a. 75 horsepower engine?

Power Problem #2 • Two physics students, Will N. Andable and Ben Pumpiniron, are in the weightlifting room. Will lifts the 50 kg barbell over his head 2. 5 meters 1 time in 6 seconds; Ben lifts the 50 kg barbell over his head 2. 4 m 1 time in 5 seconds. Which student does the most work? _______Which student delivers the most power? ______

Power Problem #3 • A 1200 Kg car accelerates from 5 m/s to 30 m/s in 4 s. Calculate the car’s horsepower.