8. A room has one 60 W, one 100 W, and one150 W light bulb. How much does it cost to use the all of the lamps for 2.5 hours at 9 cents per kWh?
To calculate the cost, we need to determine the total energy consumed by all the lamps and then multiply it by the cost per kWh.
First, we calculate the total energy consumption in kilowatt-hours (kWh) for each individual lamp:
60 W = 0.06 kW
100 W = 0.1 kW
150 W = 0.15 kW
Next, we calculate the total energy consumption of all the lamps combined:
Total energy consumption = (0.06 kW + 0.1 kW + 0.15 kW) = 0.31 kW
To determine the total energy consumed in 2.5 hours, we multiply the energy consumption by the number of hours:
Total energy consumed = 0.31 kW x 2.5 hours = 0.775 kWh
Finally, we calculate the cost:
Cost = Total energy consumed x Cost per kWh
Cost = 0.775 kWh x $0.09/kWh
Therefore, the cost to use all of the lamps for 2.5 hours at 9 cents per kWh is $0.06975.