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## mayankdevnani 3 years ago A steam engine has an efficiency of 20%.It is given an energy of 1000 cal.per minute.What is the actual work done by it in joule and in calories? a) 100 cal,800 J b) 200 cal,873 J c)10 cal,80 J d)100 cal,100 J

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1. mayankdevnani

@amistre64 @ParthKohli @hartnn @Callsito @Zarkon @Hero @.Sam. @estudier @ganeshie8 @ajprincess @Algebraic!

2. mayankdevnani

@Callisto

3. amistre64

im not sure since we havent gone over this in my physics class yet, but i would say that 20% efficiency means that 20% of the 1000 cals are used; giving us 200 cals in the answer at least

4. SheldonEinstein

May I help?

5. amistre64

please do :)

6. mayankdevnani

ofcourse @SheldonEinstein

7. SheldonEinstein

;) OK so first of all what @amistre64 discussed in his previous comment is very imp. to do this quest., so @mayankdevnani do you know what does efficiency mean?

8. mayankdevnani

ok @amistre64 then

9. mayankdevnani

yaa

10. mayankdevnani

efficiency=winout/winin*100

11. mayankdevnani

right @SheldonEinstein

12. SheldonEinstein

Yeah or in simpler words it is : $$\large{\frac{\textbf{Output}}{\textbf{Input}}\times 100}$$ it is 100%...

13. mayankdevnani

yaa

14. SheldonEinstein

So, what we have is output/input * 100% = 20% , correct?

15. mayankdevnani

correct

16. SheldonEinstein

Ok so now, let me understand the second line of the quest. , is the output = 1000 calorie ?

17. mayankdevnani

yaa

18. mayankdevnani

then

19. mayankdevnani

@SheldonEinstein then

20. SheldonEinstein

Oh sorry wait!

21. mayankdevnani

yaa

22. SheldonEinstein

I am getting diff. answer so I am checking it, sorry , it will require some patience.

23. mayankdevnani

ok

24. SheldonEinstein

Quest. is wrong

25. mayankdevnani

why?? no it is right

26. SheldonEinstein

Time is not given.. though if you take 1 minute it is 200 cal.

27. mayankdevnani

yaa

28. SheldonEinstein

See , Power = 1000 cal/minute (given)

29. SheldonEinstein

use this and you will get 200 cal. as answer.

30. mayankdevnani

so what's the work done?

31. SheldonEinstein

W = P * time if T = 1 second , W = P ... that's it , find P(output) .. (using efficiency = Ouput/Input *100%) in Cal. per minute , that will be your answer

32. SheldonEinstein

200 cal.... = WORK DONE

33. mayankdevnani

no

34. mayankdevnani

but the work done is in joule

35. mayankdevnani

@ParthKohli @Preetha

36. mayankdevnani

@SheldonEinstein

37. mayankdevnani

@myininaya

38. SheldonEinstein

Is my answer correct, i.e. 200 cal, 873 J ?

39. mayankdevnani

yaa

40. SheldonEinstein

So where is the problem? ?? ? ?

41. mayankdevnani

873 J how??

42. mayankdevnani

@amriju

43. mayankdevnani

@SheldonEinstein how you got it 873J

44. SheldonEinstein

I got 200 Cal, and it is in options, soo....

45. mayankdevnani

but it's wrong

46. mayankdevnani

i need solution

47. mayankdevnani

can you help me @amriju

48. SheldonEinstein

200 cal * 4.184 = 836 J (approx. ) not equal to 873 Joule , hence I think the options are wrong..

49. mayankdevnani

no it was not wrong

50. amriju

work done is 20 percnt of the energy given...thats efficiency....so per minute is 20percnt of 1000 cal...thats 200 cal...convert to joules

51. mayankdevnani

so 1cal.=? j @amriju

52. amriju

4.2...approx..the correct is 4.187...

53. mayankdevnani

is it 4.37

54. amriju

nope

55. mayankdevnani

why??

56. amriju

thats how it is defined...both are units...and 1 cal is defined as 4.187 joules...

57. SheldonEinstein

That is what I was saying @amriju

58. mayankdevnani

in my solution book...the answer is as follows- $\frac{20}{100}=\frac{W}{1000}=200 calorie$ OR $200\times4.37=873J$

59. mayankdevnani

is that right?? @amriju and @SheldonEinstein

60. SheldonEinstein

That is wrong, 1 Cal. = 4.187 Joule NOT 4.37 joule...

61. mayankdevnani

ok... thnx... @SheldonEinstein and @amriju

62. amriju

u may jst check on wikipedia...and its seems that none of the options are correct...the closest being 200, 837

63. amistre64

just for reference http://www.wolframalpha.com/input/?i=200+calorie+to+joule

64. amistre64

if your options are truely: 200,873 then its most likely a typo and prolly meant to be read as 200,837

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