If your computer uses 3.5 A at 110 V, how much will it cost to use the computer for 3 hours a day, seven days a week for two weeks? Assume that the cost of electricity is $0.09 for every kW•h of energy.

With steps please

1 Answer
Nov 17, 2017

OK, these 3 questions are part of a series, if I help with this one hopefully you will be able to apply the same logic to the others?


First power, #P = V xx I# but we need to make sure the units are in kW, so (like with m and km) we need to divide the number we get by 1000 as the unit is 1000 x bigger.

Secondly we need to convert the power to an energy using #E = P xx t# but here we need to convert all the times quoted into hours to get energy in kWh (normally we’d use one Joule = 1 Watt second)

Finally we need to convert the energy into a price, given that each kWh costs 9 cents.

OK, off we go!

#P = V xx I = 110 xx 3.5 = 385 W = 0.385 kW#

#E = P xx t = 0.385 xx (3 xx 14) = 16.17 kWh#

#$ = kWh xx cost = 16.17 xx 9 cents = 145.53 #cents or $1.46 approx.