1. Chapter 8
Work, Power and Energy

2. Work- applying a force over a distance; must be in the same direction
Work=Force x Distance W=Fd
Unit=Joule=Nm=kgm2/s2

3. Power-rate of doing work
Power=Work/Time P=W/t
Power=Force x Distance/Time
Unit=Watt

4. Energy- ability to do work
Mechanical Energy- energy due to motion or position of an object
Kinetic Energy- energy of a moving object
Kinetic Energy=1/2 mass x velocity2 KE=1/5mv2
Potential Energy- stored energy
Potential Energy=mass x height x acceleration due to gravity PE=mgh

5. Law of Conservation of Energy- energy cannot be created or destroyed, but can be transformed from one form to another

6. Machines- devices used to multiply forces or simply to change direction of forces
Simple Machines:
Incline Planes Levers
Screw Pulley
Wedge Wheel and Axle

12. Review Questions
1. A constant force of 20.0 N applied to an object causes it to move at a constant speed of 4.0 m/s. How much work is done on the object in 6.0 s?

13. A 10.0 kg object and a 5.0 kg object are released simultaneously from a height of 50.0 m above the ground. After falling freely for 2.0 s, the objects have different:
-accelerations
-velocities
-kinetic energies
-displacements

14. If 1375 J of work is done on a mass of 20
If 1375 J of work is done on a mass of 20.0 kg, it can be raised ________ m.

15. Work is not done when you
-pick up a box and place it on your shoulder
-support the box on your shoulder
-carry the box a distance of 15 m
-put the box on a shelf

16. A person raises a 2. 0 kg mass from the floor to 1
A person raises a 2.0 kg mass from the floor to 1.5 m above the floor in 5.0 s. If the person performs the same task again in 10.0 s instead of 5.0 s, what has changed?
-the amount of work done
-the total amount of energy involved
-the gravitational potential energy involved
-the height
-the power

17. 6. A 1. 0 kg pendulum is released from a height of 3
6. A 1.0 kg pendulum is released from a height of 3.2 m vertically from a reference level. Its potential energy is _____.

18. 7. A 5 kg cart is traveling at 12 m/s. What is its kinetic energy?

19. 8. Name 6 simple machines.

20. 9. Who is Rube Goldberg?

21. 10. Compare and Contrast Kinetic and Potential Energy.