Power Power is the rate at which work is done. Power is how fast work is done. What are the factors of power?

Power formula: POWER = WORK TIME

Power unit As is implied by the equation for power, a unit of power is equivalent to a unit of work divided by a unit of time. Thus, a unit of power is joules/second. To honor him (who?), the standard metric unit of power is also called the watt. (Who is the watt named after?)

Power Ratings Most machines are designed and built to do work on objects. All machines are typically described by a power rating. The power rating indicates the rate at which that machine can do work upon other objects. Thus, the power of a machine is the work/time ratio for that particular machine.

Horsepower For historical reasons, the horsepower is occasionally used to describe the power delivered by a machine. One horsepower is equivalent to approximately 750 watts. Note: Horsepower is NOT a metric unit!

Power, Work, Time relationship The power equation suggests that a more powerful engine can do the same amount of work in less time. Power = Work Time

A person is also a machine which has a power rating. Some people are more powerful than others; that is, they are capable of doing the same amount of work in less time OR more work in the same amount of time.

A Power Problem 1. Jack and Jill ran up the hill. Jack is twice as massive as Jill; yet Jill ascended the same distance in half the time. Who did the most work? Who delivered the most power? Explain your answers.

Jack and Jill answer Let’s suppose Jack is 60 kg (= ___ N?) Let’s suppose Jill is 30 kg (= ___ N?) Let’s suppose the hill is 10 m high. W Jack = F x d = W Jill = F x d = Who did the most work?

Jack and Jill answer, continued Suppose Jack’s time is 20 seconds and Jill’s time is 10 seconds. So, Power Jack = W/t = And, Power Jill = W/t = Who is the more powerful?

Another Power Problem 2. If little Nellie Newton lifts her 40-kg body a distance of 0.25 meters in 2 seconds, then what is the power delivered by little Nellie's biceps?

Little Nellie Newton answer Nellie’s mass is 40 kg (= ___ N) P = W = F x d t t P = (400 N) (0.25 m) 2 sec P = 50 Nm/s = 50 J/s = 50 watts = 50 W