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# Work Power and Energy

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### Work Power and Energy

1. 1. WORK  Definition  Mathematical Form  Unit  Cases of Work
2. 2. Q. What is work? A. Work is said to be done when a force acts on a body and moves it through a certain displacement. WORK d Work done by the Force F mm F
3. 3. Mathematical Form: WORK d Work done by the Force F mm F
4. 4. If force is applied on a body and it moves the body through a displacement ‘d ’, then the work 'W' is defined by the relation W = F. d We have already studied scalars and vectors. Q. What is the nature of work? A. Work is a scalar quantity. WORK
5. 5. Unit of work: The SI unit of work is joule (J). One Joule When a force of one Newton moves a body through a distance of one meter in the direction of force, then the work done is equal to one joule. WORK
6. 6. Positive Work CASES OF WORK When force and displacement are in the same direction Then  = 0° W = F d cos 0° = F d x 1 = F d
7. 7. Example Work done by the Force m m F CASES OF WORK d
8. 8. Zero Work When force is perpendicular to the displacement Then  = 90° W = F S cos 90° = F x 0 = 0 In this case work done is zero. CASES OF WORK
9. 9. Example CASES OF WORK
10. 10. When force and displacement are in the opposite direction Then  = 180° W = F d cos 180° = F d x (-1) cos 180° = -1 W = - F d CASES OF WORK Negative Work
11. 11. Condition for Negative work d W CASES OF WORK
12. 12. Q. Give an example of positive work? A. Pushing something horizontally is an example of positive work. Q. Give an example of negative work? A. Lifting something vertically upwards is an example of negative work. WORK
13. 13. Why work is Zero ?
14. 14. POWER
15. 15. • Power is measured by the amount of Work done in One Second. • If Work W is done in ‘t’ seconds, then Power Thus, • Smaller the time in which Work is done, the greater is the Power. • Power is a Scalar Quantity. • Unit of Power is Watt. • Watt is equal to Joule/second. • Watt is equal to Kgm2/s3 . • Dimension of power is M1 L2 T-3. P=W/ T
16. 16. Energy
17. 17. • Energy is the Capacity of a body to do Work. • Energy represents the total amount of Work that a Body can do. • Unit of Energy is Joule. • Joule = Kgm2/s2.
18. 18. Numerical The two springs for reversing the motion of a heald shaft each have to be stretched 15cm to put them in position with the heald shaft down. If the stiffness of each spring is 1.5N/cm find the work done in putting the springs in position. Stiffness∞ force
19. 19. Solution : Total force required to stretch each spring = 1.5×15 = 22.5N Total force = 22.5×2 = 45N Work done = f.d =45×15 Ncm =675Ncm
20. 20. Solution: W = 675÷100 Nm W = 6.75Nm W = 6.75 J
21. 21. Numerical on Power A ringframe traveller, moving in a circle of 5cm in diameter at 9000rev/min, offers a resistance to movement of 0.15N. If the frame has 240 spindles, calculate the power expended in moving the travellers.
22. 22. Solution: Distance moved by traveller in one revolution = 5¶ = 5(3.14) = 15.70cm Distance moved per second = 15.70×9000÷60 = 23.55m
23. 23. Solution: W = f.d Work done per second on each traveller = 23.55×0.15N W = 3.53J Total work done = 3.53 on each of 240 spindles per second Power expended = 847.2W
24. 24. http://www.school-for-champions.com/science/work.htm http://library.thinkquest.org/2745/data/ke.htm http://www.regentsprep.org/Regents/physics/phys02/rolcoast/ default.htm http://www.discoveryeducation.com/teachers/free-lesson- plans/elements-of-physics-energy-and-work.cfm http://www.sparknotes.com/physics/workenergypower/workpo wer/section2.rhtml http://everythingscience.co.za/grade-12/08-work-energy-and- power/08-work-energy-and-power-03.cnxmlplus http://hyperphysics.phy-astr.gsu.edu/hbase/work.html
25. 25. You don't always get what you wish for, you get what you work for.
26. 26. THANK YOU