Lesson 3 First Quarter Work and Power SCI8

A presentation about work and power

1. infer the amount of power and work possessed by an object or body. solve problems on work and power. apply the concepts of work and power in real life situations.

2. WORK AND POWER

3. Have you ever tried wishing a certain task can be done more easily?

4. Have you ever wished you can pull off a task at much lesser time?

5. As a student are you already working?

6. WORK refers to a task that is accomplished by exerting physical and mental efforts.

7. Work is done only when a force causes an object to move in the same direction as the force.

8. Identify the situations that follow in which Work is done

9. A boy pulling a cart

10. Pulling a drawer

11. A boy pushing a wall

12. A man carrying a bag of groceries

13. In symbols, W = Fxd Where: W = work (J) F = magnitude of the net force (N) d = magnitude of the displacement (m) Work can be calculated with this simple equation

14. Units of Work System Unit of Work Name of Combined Unit SI Newton-meter ( N m) joule (J) cgs Dyne-centimeter (dyne cm) erg English system Foot-pound (ft lb) Foot-pound (ft lb)

15. James Prescott Joule (1818-1889) An English physicist who studied the nature of heat and discovered its relationship to mechanical work

16. Let’s solve a problem

17. 1. How much work does a person do in pushing a box with a force of 10 N over a distance of 4.0 m in the direction of the force?

18. Given ; Net force=10 N displacement= 4.0 m Work=? PROBLEM NUMBER 1 40 J

19. 2. A weightlifter lifts barbells of 200 N above his head to a height of 2 m. How much work does he do?

20. Given ; Net force=200 N displacement= 2 m Work=? PROBLEM NUMBER 2 400 J

21. 3. Find the distance travelled of a box if the work done is 50 joules and the force exerted is 15 N.

22. Given ; Net force=15 N Work= 50 J displacement=? PROBLEM NUMBER 3 3.333 m

23. 4. It took 50 joules to push a chair 5 meters across the floor. With what force was the chair pushed?

24. Given ; displacement= 5 m Work= 50 J Net force=? PROBLEM NUMBER 4 10 N

25. 4. H ow much work is needed to lift a 2 kg box to a height of 3 m above the ground?

26. Given ; M ass = 2 kg Height = 3 m Work? PROBLEM NUMBER 5 58.8 J

27. Summary Of Formula

28. “With great POWER comes great Responsibility ”

29. POWER is the rate of doing work

30. UNITS OF POWER Power is measured in joules per second (J/s) or WATTS (W). The unit of power is J/s also known as watt, a unit named after James Watt, the inventor of the “steam engine ”

31. A common units used by electric power companies is the kilowatt (kW). 1watt (W) = 1 joule/second 1 kilowatt (kW) = 1 000 watts

32. It is often used to measure the power of engines.

33. He showed that 1 horsepower= 550 ft.lb/s

34. 1. How much power was exerted to accomplished 350 Joules of work in 30 seconds?

35. Given ; Work= 350 J time= 30 s Power=? PROBLEM NUMBER 1 11.666 W

36. 2. If a body builder does 6000 J of work in 1 minute and 15 s, what is his power output?

37. Given ; Work= 6000 J time= 1 minute & 15 s Power=? PROBLEM NUMBER 2 80 W

38. 3. A 40-W light bulb dissipated 240000 Joules of energy, how long has it been burning?

39. Given ; Power= 40 W Work = 240,000 J of energy time=? PROBLEM NUMBER 2 6,000 seconds

40. Any Questions?