Question

The cost of electricity varies widely throughout the United States; $0.120/kWh is a typical value. At this unit price, calculate the cost of the following.
a. Leaving a 40.0-W porch light on for 2 weeks while you are on vacation.
b.Making a piece of dark toast in 3.00 min with a 980 W toaster.
c. Drying a load of clothes in 40.0 min in a 4900 W dryer.

Answer 1

Answer: a) $1.6123 , b) $0.00588 c) $0.392

Explanation:

Note, all power in watts is converted to kilowatts and all units of time is converted to hours.

The cost of electricity is $0.12 for 1kwh.

Question a.

Power = 40w to kilowatts = 40/1000 = 0.04kw

Time = 2 weeks to hours = 24 * 14 = 336 h.

Energy = power * time.

Energy = 0.04 * 336 = 13.44kwh.

If 1kwh cost $0.12, then 13.44 kwh will cost

0.12 * 13.44 = $1.6132.

Question b

Power = 980w to kilowatts = 980/1000= 0.98kw

Time = 3 minutes to hours = 3/60 = 0.05 h

Energy = power * time

Energy = 0.98 * 0.05

Energy = 0.049kwh

If 1kwh cost $0.12, then 0.049 kwh will cost

0.049 * 0.12 = $0.00588

Question c

Power = 4900w to kilowatts = 4900/1000= 4.9kw.

Time = 40 minutes to hours = 40/ 60 = 0.67.

Energy = power * time

Energy = 4.9 * 0.67

Energy = 3.267 kwh

If 1 kwh cost $0.12, then 3.267kwh will cost

3.268 * 0.12 = $ 0.392