1. Work and power And you

2. Work = Force x parallel displacement = F x d Units of Work = Joules = N x m

3. Power = rate at which work is done = Work/time = Joules /sec = Watts Power plants in Boulder must must be able to provide large amounts of E at peak times Bill at end of month in Kilowatt hours = 1000 J/s (3600 s) = 3.6x10 6 J = 1KwHr Note Joule is a unit of Energy not power – so you really get an Energy used bill

4. Application of this knowledge Light bulb uses ~ 60 watts of E (60 J/s) Florescent bulb ~ 10 watts Electric car ~ 35KW at peak demand

5. Horsepower = Avg. amount of work a horse can do = 550 ft. x lbs. / sec = 746 W 746W = 1HP

6. Efficiency (e) e = E out / E in Therefore value is always less than 1 0.6 = 60% efficient

7. Efficiency question: A car produces 200 HP and uses 1L of gas/min. The heat of combustion of the fuel is 46,000 J/ml. What is the efficiency of the car???? Define E out and E in Keep in mind units of E Common units on numerator and denominator Joules

8. e = E out/E in e = (200 HP)(746 W/HP)(60s/L) = (46,000 J/ml)(1000 ml/L) (200 HP)(746 J/s/HP)(60s/L) = (46,000 J/ml)(1000 ml/L) =.19 = 19%

9. Beep