1. Lesson 5.4 Power Essential Question: How do you calculate power?

2. What is power? The rate at which work is done The rate of energy transfer by any method

3. Technical Definition Power is a quantity that measures the rate at which work is done or energy is transformed

4. How do you find power? Power equals work divided by time interval

5. Power Alternative Formula Power equals force times speed

6. How is power measured? The SI unit of power is the watt, W, which is one joule per second. The horsepower, hp, is another unit of power. One horsepower equals 746 watts.

7. Motors & Power The power output for every motor is different. As a result, motors will do work at different rates and transfer energy at different rates.

8. A 193 kg curtain needs to be raised 7.5 m, at a constant speed, in as close to 5.0 s as possible. The power ratings for three motors are listed as 1.0 kW, 3.5 kW, and 5.5 kW. Which motor is best for the job?

9. Two horses pull a cart. Each exerts a force of 250.0 N at a speed of 2.0 m/s for 10.0 min. a.Calculate the power delivered by the horses. b.How much work is done by the two horses?

15. A 50.0 kg student climbs 5.00 m up a rope at a constant speed. If the student’s power output is 200.0 W, how long does it take the student to climb the rope? How much work does the student do?

16. A motor-driven winch pulls a 50.0 kg student 5.00 m up a rope at a constant speed of 1.25 m/s. How much power does the motor use in raising the student? How much work does the motor do on the student?

17. How do you calculate power?