1. 5.5 P OWER P. 250-254

2. Power equals the amount of work done divided by the time interval during which the work is done. Power

3. When carrying a load up some stairs, you do the same amount of work whether you walk or run up the stairs. Power is the rate at which work is done. Power

4. A high-power engine does work rapidly. An engine that delivers twice the power of another engine does not necessarily produce twice as much work or go twice as fast. Twice the power means the engine can do twice the work in the same amount of time or the same amount of work in half the time. A powerful engine can get an automobile up to a given speed in less time than a less powerful engine can. Power

5. The unit of power is the joule per second, also known as the watt. One watt (W) of power is expended when one joule of work is done in one second. One kilowatt (kW) equals 1000 watts. One megawatt (MW) equals one million watts. Power

6. think! If a forklift is replaced with a new forklift that has twice the power, how much greater a load can it lift in the same amount of time? If it lifts the same load, how much faster can it operate? Answer: The forklift that delivers twice the power will lift twice the load in the same time, or the same load in half the time. Power

7. P OWER  Power (P) - the rate at which work is done, or the rate at which energy is transferred.  The formula for power is:

8. W ATT The SI unit of power is the Watt (W), named in recognition of James Watt’s contributions to physics. A power output of 1 W results when 1 J of work is done per second.

9. A 100-W light bulb has a power output of 100 W: it transfers energy at a rate of 100 J/s. One watt is a very small power output, so the kilowatt (kW) is often used to measure power:

10. S AMPLE PROBLEM 1 An elevator and its occupants have a mass of 1300 kg. The elevator motor lifts the elevator to the 12th floor, a distance of 40.0 m, in 74.8 s. What is the average power output of the elevator motor?

12. Energy consumption is the conversion of produced or stored energy through useful tasks into (primarily) heat. The law of conservation of energy states that energy is not really consumed. Energy never disappears. It can, however, change from a particularly useful form into heat, which is hard to capture and control.

13. We can calculate the energy consumed of any device by rearranging out equation:

14. S AMPLE PROBLEM During a practice, a musician uses a 500-W guitar amplifier for 10 min and a 320-W keyboard amp for 30 min. How much energy is consumed?

15. T HE KILOWATT HOUR The joule is the SI unit used to measure energy. A joule per second, or watt, is used to measure power. The kilowatt hour (kWh) is a larger unit of energy used by electric utilities to measure energy consumption.

16. S AMPLE PROBLEM An old 17-cubic-foot (480 L) frost-free refrigerator uses 450 W when it is running. Assume the refrigerator runs 5.0 h each day. (a) Determine the amount of energy consumed in a day of use, in joules and in kilowatt hours. (b) Determine the annual energy consumption in kilowatt hours.

18. = 365 x 8.1 x 10 6 J = 3.0 x 10 9 J

19. Section 5.5 Calculating Energy Rating and Cost What is the cost of operating a 1100 W microwave oven for 5.0 min if the price of electrical energy is 6.0¢/kWh? Use the red data from the problem to fill in the given information. Then, use the blue variables to complete the formula below. Click the screen for a hint. powertime interval Required: ΔE; then cost price of electrical energy = Given: P =Δt = Analysis:=

20. Section 5.5 Calculating Energy Rating and Cost What is the cost of operating a 1100 W microwave oven for 5.0 min if the price of electrical energy is 6.0¢/kWh? Use the red data from the problem to fill in the given information. Then, use the blue variables to complete the formula below. Click the screen for a hint. powertime interval Required: ΔE; cost price of electrical energy = Given: P =Δt = Analysis:= 1100 W 5.0 min 6.0¢/kWh P ΔEΔE ΔtΔt

21. Section 5.5 Calculating Energy Rating and Cost What is the cost of operating a 1100 W microwave oven for 5.0 min if the price of electrical energy is 6.0¢/kWh? Use the red data from the problem to complete the calculation. Then, complete the final statement. = ()()(1 KW/1000W)(1h/60 min ) ΔE = kWh Solution: P = ΔtΔt ΔE = PΔt cost =kWh ( ) cost = ¢ ΔEΔE Statement: It coststo operate a 1100 W microwave oven for 5.0 min.

22. Section 5.5 Calculating Energy Rating and Cost What is the cost of operating a 1100 W microwave oven for 5.0 min if the price of electrical energy is 6.0¢/kWh? Use the red data from the problem to complete the calculation. Then, complete the final statement. = ()()(1 KW/1000W)(1h/60 min) ΔE = kWh Solution: P = ΔtΔt ΔE = PΔt cost =kWh ( ) cost = ¢ ΔEΔE Statement: It coststo operate a 1100 W microwave oven for 5.0 min. 1100 W 5.0 min 0.092 6.0¢/kWh 0.55 0.55¢

23. H OMEWORK P. 251 practice #1-3 P. 252 practice #1 P. 253 practice #1 P. 254 questions #1,2,4,5

24. Ch. 5 Review P.261 ch. 5 self quiz #1-15 P. 262-267 ch. 5 review #1-23, 25-40, 42-44, 47,49-51, 57, 59 Unit review ch. 5 P. 363 -363 unit self quiz #1-6, 18-23, P. 364-371 #1-7, 33-42, 44, 45, 47, 73, 74, 79