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As a store manager, would you prefer to hire a clerk who could unload a truck in one hour, or a second clerk that could unload a truck in half an hour? If the employees did the same amount of work unloading the truck, what was the difference? Time Power – is the rate at which work is done In other words, how fast or slow is the work done Watt is the unit for power 1 watt is equal to 1 joule of work done in 1 second Make note of units, if time is not in seconds, it must be converted. Remember that W=Fd, so P= If , then P=F*v. (F*d) t . In physics, when you see the word power you should think: power is the energy used by the time it takes to do the work. The watt was named after James Watt (17361819), the Scottish engineer who invented the steam engine. Another unit of power that is often used for engine power is the horsepower. Watt expressed the power of his engines as the number of horses an engine could replace. One horsepower is equal to 746 watts. Who has more power? P=w/t P= (100*2)/1 P= 200 W P= (100*2)/10 P= 20 W A motor does 5,000 joules of work in 20 seconds. What is the power of the motor? A motor does 5,000 joules of work in 20 seconds. What is the power of the motor? W= 5,000 J t= 20 s P= ? P= 5,000/20 P= 250 W A machine does 1,500 joules of work in 30 seconds. What is the power of this machine? A machine does 1,500 joules of work in 30 seconds. What is the power of this machine? W= 1,500 J t= 30 s P= ? P= 1,500/30 P= 50 W