Question

A standard flashlight battery can deliver about 4.9 W·h of energy before it runs down. (a) If a battery costs 80 cents, what is the cost in dollars of operating a 100 W lamp for 11 h using batteries? (b) What is the cost in dollars if power is provided at the rate of 6.0 cents per kilowatt-hour?

Answer 1

GIVEN DATA

ENERGY THAT BATTERY CAN DELIVER IS E = 4.9 W·h

POWER P = 100W

TIME      T = 11 h

WE KNOW THAT ENERGY = POWER*TIME

then ENERGY = 100*11 = 1100 Wh

A) FOR 4.9 W h cost is US$0.80

          1100 Wh cost will be (1100/4.9)*0.80

                                      = US$179.59

b) given that  US$0.06 per kilowatt-hour

    US$0.06 for on 1000 Wh

    for 1100 Wh the cost will be  US$0.06 *1100/1000  

                                        =  US$0.066