## mayankdevnani 3 years ago State that WORK is DONE or NOT..... A Wind-Mill is lifting water from a well. and also justify your answer..

1. mayankdevnani

am confusing.....plz help me

2. VV-EFF

for windmill work is not done and for water work is done!

3. mayankdevnani

no @VV-EFF question is one!!

4. mayankdevnani

@sirm3d

5. VV-EFF

work is done then! because windmill is applying force to pull up the water and the water itself displaces! now it depends on the angle between the force applied by the mill and the direction of water!

6. mayankdevnani

yaa.. i know but my teacher says the work done is zero..

7. VV-EFF

she would be considering cosQ =0, then she's right

8. mayankdevnani

can you help me @ganeshie8 and @gerryliyana

9. mayankdevnani

what is this? i can't understand

10. VV-EFF

workdone=FxDxcos(Q) where Q is the angle between the force F and displacement D.

11. gerryliyana

the work done is zero., because windmills always return to the original point

12. mayankdevnani

how can we know that angle is of cosQ

13. VV-EFF

yeah thats the point @gerryliyana ! he is considering water anf mill, both as a system!

14. VV-EFF

and in case of water ! water is displaced by force!

15. mayankdevnani

work is done then! because windmill is applying force to pull up the water and the water itself displaces! now it depends on the angle between the force applied by the mill and the direction of water! @gerryliyana in this case!!

16. gerryliyana

nice @VV-EFF

17. mayankdevnani

so in that case...

18. VV-EFF

nice What! @gerryliyana ! gve him the answer man! lol....

19. mayankdevnani

so finally whats the conclusion of this answer.

20. mayankdevnani

@Aperogalics have a look!!

21. VV-EFF

the conclusion is that if u are considering the both as a system then the work is done ; iff Q is not equals to 1.5707. and if the system is only the mill then the work is said to be not done!!

22. mayankdevnani

but the answer is to be written is one

23. VV-EFF

work is not done! then

24. mayankdevnani

in my solution book answer is work is done and the reason is that windmill pulls the water against the gravity...

25. Aperogalics

@mayankdevnani there are two thing work done by the system and work done on the system here if the system is windmill then work done by the system is zero as there is no net dispacement while work done by the system is +ve as he make the water to be displaced........:)

26. VV-EFF

obviously !!!!! @mayankdevnani if its against the gravity the according to the equation F=ma , water has mass and the acceleration is .9.8 mLsecsquare! then the force definitely exists ! and so the workdone!

27. mayankdevnani

28. VV-EFF

now dude stop confusing your self! the answer is that the work is certainly done by the system!

29. mayankdevnani

m really confused @Aperogalics and @VV-EFF what is the concluded answer and answer should be one means both work done or not

30. mayankdevnani

so i am correct and my teacher is wrong!!!

31. VV-EFF

yeah!

32. VV-EFF

work is done by the system! its certain!

33. mayankdevnani

34. VV-EFF

yeah!

35. mayankdevnani

let @Aperogalics be write and then think,. he has creative mind...let @Aperogalics be answer

36. Aperogalics

@mayankdevnani @VV-EFF is very clever he is still saying work is done by the system if ur mam is talking about work done on the system then she is correct and if not then you are correct.........:)

37. mayankdevnani

no my mam says that the work be zero and i say that work is not zero @Aperogalics

38. VV-EFF

39. Aperogalics

@mayankdevnani yes ur mam says work is zero but is it by the system or on the system??????????? do you know about which she was talking about??????????????

40. mayankdevnani

no.. my friend george said that mam says the work done is zero

41. mayankdevnani

and also 1 thing

42. mayankdevnani

my senior friend also says that _____ "lifting water" is the work that is done. When anything is lifted - it is moved (displaced) upward against the force of gravity. The force that lifts the object (water) must be greater that that of gravity or the object won't displace upward. The Net force that acts upward to lift (object, water, etc) multiplied by the vertical lift height is defined to be the work done in this process.

43. mayankdevnani

secondly, there are not more than one work done... right..

44. mayankdevnani

lastly , what's the concluded answer suppose you are in examination hall and you have a pen and this question ...how would you solve it? @Aperogalics and @VV-EFF

45. VV-EFF

i would say that u plz read the conversation above! and conclude the answer urslf!

46. Aperogalics

@mayankdevnani answer my question and you will get the answer by yourself:)

47. mayankdevnani

plz

48. Aperogalics

a basic question in every book suppose a man lifts a box to his head and walk 40kms . IS THE WORK DONE BY THE PERSON?

49. mayankdevnani

no work done is zero

50. Aperogalics

why????????

51. Aperogalics

@mayankdevnani

52. mayankdevnani

because force acts in perpendicular direction\[90^{0}\] and displacement is at right angle

53. mayankdevnani

right @Aperogalics

54. Aperogalics

is the work is done against gravity?????

55. mayankdevnani

|dw:1352199535611:dw|

56. mayankdevnani

no @Aperogalics

57. Aperogalics

why?????

58. mayankdevnani

59. Aperogalics

yes that's the thing force is applied against gravity and displacement is zero here|dw:1352199714164:dw| there displacement is in perpendicular direction and here no displacement

60. Aperogalics

getting it???????

61. Aperogalics

@mayankdevnani

62. mayankdevnani

thnx... i get it

63. Aperogalics

always for you help here i asked 2 different question bith r work but done by different systems.....k:) so if the question is of IIT then it will mention the system otherwise my first post is the answer:)

64. SheldonEinstein

I will say a small thing that "pulley" is the main thing here... |dw:1352284103729:dw|

65. gerryliyana

nice @SheldonEinstein

66. SheldonEinstein

THanks @gerryliyana :)

67. mayankdevnani

@SheldonEinstein so that the work done is zeroo..you would say that

68. SheldonEinstein

I had said that and yes Work done is ZERO! (if we are talking about a diff. kind of system)