1. WORK and ENERGY Work Kinetic Energy Work Energy Theorem
Potential Energy
Conservation of Energy
Power

2. WORK Work is a transfer of energy
Force causing an object to have a displacement
Maximum work: F and d are parallel
Minimum work: F and d are perpendicular
W = Fd
Units: N∙m
SI Units: Joules (J)
Scalar
Independent of pathway

3. WORK Importance of sign + W: F and d are in the same direction
- W: F and d are in the opposite direction

4. WORK
Hewitt Physics

5. WORK
Graphing Work
Area under the curve of the F vs. d graph.

6. Independent of pathway
WORK
Independent of pathway

7. ENERGY Ability to do work Two types
Kinetic Energy
Potential Energy
Heat measures the transfer of energy.

8. KINETIC ENERGY Energy of motion KE = ½ m v2 Units: kg m2 / s2 = Joule
Scalar
Work-Energy Theorem
Net work is equal to the change in energy
W =  KE
Fd = KEf - KE°
Fd = ½ m vf2 - ½ m v°2 = ½ m (vf2 - v°2)

9. Pg 184 #1-22 No Yes +; no; Yes +; yes –
No; force decrease, distance increase; work constant
Tension and Weight are perpendicular so no work
Longer skids are moving faster
Yes; no; yes; weight and air resistance
53 J; - 53 J
2.4 x 105 J
47.5 J
10) 6230 J; J; 0.640
11) no, yes, yes
12) no; mass is + and v is squared
13) yes; depends on the distance
14) 1 to 25
15) No work; motion and force are perpendicular
16) Speed double; work is quadrupled…140 m.
17) To climb work must be done against gravity.
18) Work done by friction equals particle speeds decrease.

10. POTENTIAL ENERGY Store energy Able to do work later
Units: kgm2/s2 = Joules
Scalar
Two main types
Gravitational potential energy
Elastic potential energy

11. GRAVITATION POTENTIAL ENERGY
Energy possessed by object because of its position in a gravitational field.
W = Fd
PE = mgh
Zero Gravitation Potential Energy is the point of reference

12. Pg 172 Sec Rev; pg 185 23-25 4.4 x 10-3 J 2.8 m/s 6.18 x 10-2 J
Kinetic; nonmechanical; kinetic, gravitational; elastic potential
Answers vary
23) a) 5400 J, 0 J, 5400 J
b) 0 J, J; 5400 J
c) 2700 J, J, J
24) –19.6 J; 39.2 J; 0 J
25) J; J; 0J

13. ELASTIC POTENTIAL ENERGY
Potential energy stored in the deformation (compression or stretched) of an elastic object.
Hooke’s Law
Restoring force
F = -kx
W = Fd
PE = ½ k x2
Units: kg m2 / s2 = Joule

14. CONSERVATION OF ENERGY
First Law of Thermodynamics
Energy is never created or loss; it is just transfer from one form to another.
Energy before = energy after in an isolated system.
Second Law of Thermodynamics
Transfer of energy
Mechanical Energy is the total energy
TE = KE + PE (conserved)
TE = KE + PE + Wf (not conserved)

15. CONSERVATION OF ENERGY
Energy is never created or loss; it is just transfer from one form to another.
Energy before = energy after in an isolated system.
Mechanical Energy is the total energy
TE = KE + PE (conserved)
TE = KE + PE + Wf (not conserved)

16. Pg 186 #26-34, 37 30) KE max at the bottom; PE max at the top
31) No, energy is not conserved
32) Gravitational and elastic; conservation of energy.
33) 12.0 m/s
34) 10.9 m/s; 11.6 m/s
37) J; J; 2.43 m/s; J, 0.211J
26) nonmechanical; mechanical; mechanical; mechanical; both
27) KE Max at bottom
PE Max at top; KE becomes PE going up and PE becomes KE going down
28) Conservation of energy and will not hit the instructor; give a push then it will hit
29) Does work on it to move up; no work, d = 0; does negative work against gravity

17. CONSERVATION OF ENERGY
Hewitt Physics

18. CONSERVATION OF ENERGY
Hewitt Physics

19. NEXT-TIME QUESTION
                    Three baseballs are thrown from the top of the cliff along paths A, B and C. If their initial speeds are the same and there is no air resistance, the ball that strikes the ground below with the greatest speed will follow path 

20. NEXT-TIME QUESTION
Two smooth tracks of equal length have, "bumps" - A up, and B down, both of the same curvature.
If two balls start simultaneously with the some initial speed, the ball to complete the journey first is along
If the initial speed equals 2 m/sec, and the speed of the ball at the bottom of the curve on Track B is 3 m/sec, then the speed of the ball at the top of the curve on Track A is

21. POWER Rate work is done or which energy is transferred P = W / t
= Fd / t
= F v
Units: J/s = Watts (W)

22. CONCEPTS
As a consultant to the soft-drink industry, Dr. J is given the task of conducting the ultimate Pepsi taste test. This is Dr. J's tenth taste test, which puts him seven up on his nearest consultant, who had only done three. Of course Dr. J is very qualified, having been hooked on soft drinks (especially orange soda) since he was Nehi to a pop bottle. Dr. J mounts a rather large container of Pepsi on a ledge some 3 meters above the ground. A bullet of mass 5 grams is then fired into the container, thus killing the taste. Not only that, but the Pepsi falls through the bullet hole onto the ground below (causing the taste to go flat). The wall of the container is 2 cm thick. The velocity of the bullet changes from an initial value of 500 m/sec just before striking the container wall to 5 m/sec upon leaving the container wall and entering the Pepsi. It finally fizzles out at a point 25 cm from the container wall.       
A. How much work does the container wall do on the bullet?
How much work does the Pepsi do on the bullet?
At what velocity does the Pepsi hit the floor?

23. Chapter 10: R pg 199
1) A force of 825 N is needed to push a car across a lot. Two students push the car 35m.
a) How much work is done?
b) After a rainstorm, the force needed to push the car doubled because the ground became soft. By what amount does the work done by the students change?
29000J; work doubles

24. Chapter 10: R pg 199
2) A delivery clerk carries a 34 N package from the ground to the fifth floor of an office building, a total height of 15 m. How much work is done by the clerk?
510 J
3) What work is done by a forklift raising a 583 kg box 1.2 m?
6900 J

25. Chapter 10: R pg
4) You and a friend each carry identical boxes to a room one floor above you and down the hall. You choose to carry it first up the stairs, then down the hall. Your friend carries it down the hall, then up another stairwell. Who does more work?
Same amount of work
5) How much work does the force of gravity do when a 25 N object falls a distance of 3.5 m?
88 J

26. Chapter 10: R pg 202
6) An airplane passenger carries a 215 N suitcase up stairs, a displacement of 4.20 m vertically and 4.60 m horizontally.
a) How much work does the passenger do?
b) The same passenger carries the same suitcase back down the same stairs. How much work does the passenger do now?
903 J; -903 J
7) A rope is used to pull a metal box 15.0 m across the floor. The rope is held at an angle of 46.0 ° with the floor and a force of 628 N is used. How much work does the force on the rope do?
6540 J

27. Chapter 10: R pg
8) A worker pushes a crate weighing 93 N up an inclined plane, pushing horizontally, parallel to the ground in the figure.
a) The worker exerts a force of 85 N. How much work does he do?
b) How much work is done by gravity?
c) The coefficient of friction is = How much work is done by friction?
340 J; -279 J; 130 J

28. Answers: Chapter 10 1) 800 J 2) 12000 J 3) 59.9 kg 4) 1.86 x 105 J
6) 25 N/m; 0.50 J
7) 600 J
8) 826 J; 1.13 x 10 4 J; x 10 4 J
9) 1.20 x 10 4 J
10) 58.7 degrees
11) 1.8 x 10 4 J
12) no work
13) 7.7 J
14) 518 J

29. Chapter 10: R pg
9) A box that weighs 575 N is lifted a distance of 20.0 m straight up by a rope. The job is done in 10.0 s. What power is developed in watts and kilowatts?
1150 W; 1.15 kW

30. Chapter 10: R pg 203
10) A rock climber wears a 7.50 kg knapsack while scaling a cliff. After 30.0 min, the climber is 8.2 m above the starting point.
a) How much work does the climber do on the knapsack?
b) If the climber weighs 645 N, how much work does she do lifting herself and the knapsack?
c) What is the average power developed by the climber?
600 J; 5900 J; 3.3 W

31. Chapter 10: R pg 203
11) An electric motor develops 65 kW of power as it lifts a loaded elevator 17.5 m in 35.0s. How much force does the motor exert?
1.3 x 105 N

32. Chapter 10: R pg 203
12) Two cars travel the same speed, so that they move 105 km in 1 h. One car, a sleek sports car, has a motor that delivers only 35kW of power at this speed. The other car needs its motor to produce 65 kW to move the car this fast. Forces exerted by friction from the air resistance cause the difference.
a) For each car, list the external horizontal forces exerted in it, and give the cause of each force. Compare their magnitudes.
b) By Newton’s third law, the car exerts forces. What are their directions?
c) Calculate the magnitude of the forward frictional force exerted by each car?
d) The car engines did work. Where did the energy they transferred come from?
Road on car; air on car; 1200 N; 2200N; chemical energy

33. Answer Chapter 10: pg214 15) 7400J 16) 800 J; 600 J
17) x 10 3 J; no work; 5.53 x 10 3 J; no; 2.2 kW
18) 9000 J; kW
19) 348 W; 696 W
20) 220 J; 110W
21) 110 kJ; 3.14 kW
22) 1.8 x 10 4 J; 2.3 kW
23) 160 W

34. Answer Chapter 10: pg214 24) 54.7 m 25) 368 W 26) 90 kW 27) 2890 N

35. Chapter 10: R pg 203
12) Two cars travel the same speed, so that they move 105 km in 1 h. One car, a sleek sports car, has a motor that delivers only 35kW of power at this speed. The other car needs its motor to produce 65 kW to move the car this fast. Forces exerted by friction from the air resistance cause the difference.
a) For each car, list the external horizontal forces exerted in it, and give the cause of each force. Compare their magnitudes.
b) By Newton’s third law, the car exerts forces. What are their directions?
c) Calculate the magnitude of the forward frictional force exerted by each car?
d) The car engines did work. Where did the energy they transferred come from?
Road on car; air on car; 1200 N; 2200N; chemical energy