A central air conditioner uses 4.5 kilowatts. It runs for 10 hours over the course of a day. How much energy does the air conditioner use during that day?

So we want to know how much energy does an air conditioner use during the day if it runs for 10 hrs and it uses 4.5 kW. So per one hour the air conditioner uses 4.5 kW/h, in other words, it uses 4.5 kW of power in one hour. In 10 hrs it uses 10 times as that or 45 kW. So the correct answer is the air conditioner would use 45 kW during that day.