Work is defined as the transfer of energy through motion when a force causes an object to move in the direction of the force. Power is defined as the rate at which work is done and is calculated by dividing work by time. The document provides examples of situations where work is and isn't being done and defines the formula for calculating work as well as the units of work and power. It also provides an example calculation of power required to move an object a given distance over time.

1. Notes: Work and Power H: Review Worksheet 5.1

2. Work and Power April 6, 2009

3. Objectives Recognize the difference between the scientific and ordinary definitions of work. Identify where work is being performed in a variety of situations. Define and calculate work and power.

4. Work Work is the transfer of energy through motion. In order for work to take place, a force must cause an object to move in the direction of the force.

5. What’s work? A scientist delivers a speech to an audience of his peers. A body builder lifts 350 pounds above his head. A mother carries her baby from room to room. A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag to her car? No No No Yes Yes

6. There are two factors to keep in mind when deciding when work is being done: something has to move the motion must be in the direction of the applied force.

7. Work is done on the books when they are being lifted, but no work is done on them when they are being held or carried horizontally.

9. Direction of Force Direction of Motion

10. Direction of motion Direction of Force

11. Formula for work Work = Force x Distance One newton-meter is equal to one joule So, the unit of work is a joule

12. Power Power is the rate at which work is done. Power = Work * /Time * (force x distance) The unit of power is the watt.

13. 1 horsepower = 550 ft lbs / sec or 746 Watts

14. Check for Understanding Two physics students, Ben and Bonnie, are in the weightlifting room. Bonnie lifts the 50 kg barbell over her head 10 times in one minute; Ben lifts the barbell the same distance over his head 10 times in 10 seconds. Which student does the most work? Which student delivers the most power?

15. Ben and Bonnie do the same amount of work; they apply the same force to lift the same barbell the same distance above their heads. Ben is the most powerful since he does the same work in less time.

16. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? Force = Mass x Acceleration Work = Force x Distance Power = Work/Time

17. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? Force = Mass x Acceleration Force = 10 kg x 2 m/s/s Force = 20 N Work = Force x Distance Work = 20 N x 10 m Work = 200 Joules Power = Work / Time Power = 200 J / 5 s Power = 40 watts