## heena 3 years ago ok they had given pendulum done 100 oscillation its amplitude reduced to 1/3 of initial value. what will be its amplitude if it completes 200 oscillation

1. JamesJ

100 oscillations in what time period?

2. heena

dont solve just tell me ur vies dat how will u suppose to handle this ques plz plz but dont solve

3. heena

*view they didnt give time period so we can assume it constant??

4. JamesJ

I still don't understand the question. Is it this: "In a given time period a pendulum completes 100 oscillations. "Then the pendulum has its amplitude decreased by 1/3 and it completes in the same time period 200 oscillations." If so, what's the question here.

5. heena

no they didnt said anything abu time period even i m asking can we assume it constant

6. JamesJ

What is true about a pendulum is that if you increase the angle of maximum oscillation more than about 10 degrees, the period of the pendulum increases. The reason for that is in calculating the standard period of pendulum, we use a small angle approximation $\sin\theta \approx \theta$ which only holds for small angles $$\theta$$. The wikipedia article has good animation of what happens when $$\theta$$ gets large and there you can see the period increases. http://en.wikipedia.org/wiki/Pendulum#Period_of_oscillation This would explain the effect described in this set up.

7. heena

but james my ques how i m gonna solve it ? any hint or idea even i m trying hit and try but u can tell ur one too that it might like dis?

8. heena

u guys have any idea?

9. heena

it is saying that when pendulum completes its 100 oscilation its amplitude reduced to 1/3 of its inital means 2/3 is remain of apmlitude i guess and then they are asking if it completes 200 oscilation than what will be the value of amplitude

10. hosein

i think amplitude decrease

11. heena

i need a value too.. :P

12. JamesJ

Oh, I see. Precisely what is the amplitude, in angular terms. Use the first couple of terms of this expansion:

13. heena

god.. u r kidding james by showin me dat short formula rit ...

14. heena

i thinks in that i m not getting they are squaring or wat?? inside the bracket?

15. Shayaan_Mustafa

hello. i am back.

16. hosein

with 100 oscillation amp 1/3 decrease so with 200 oscillation again decrease 1/3 im not sure

17. JamesJ

You know that T decreases by a factor of a 1/2. Use that formula to find what value of theta_0 will make that happen.

18. Shayaan_Mustafa

may i help here? May i could do something?

19. heena

yea solve diss ques

20. Shayaan_Mustafa

ok wait. let me analyze.

21. heena

i wasted 15mins in this ques yar

22. heena

plz quick

23. hosein

james formula is correct?

24. heena

yea but unable to aplly a i nvr heard abu dat one

25. hosein

james formula abu period of oscillation,not amplitude

26. Shayaan_Mustafa

now what i understand. BUT THIS QUESTION LOOKS INCOMPLETE. look here first calculate time period using T=1/f T=1/100 T=0.01sec

27. heena

guys i need the ans 1/9 nw think ow can we get

28. heena

f=? y u put ocilation??

29. hosein

idont understand u'r sentence?

30. heena

i mean the ans of this ques is 1/9 now just hit and try to get this ans

31. hosein

how can you got it?

32. heena

no i dont got dat i had ans key :) and my ans is not matching dats why i ask for help..

33. Shayaan_Mustafa

now use the displacement equation, y=Asinwt where w is the frequency. y=(1/3) sin(100*0.01) y=(1/3)(0.0174) y=0.005m now use this displacement as, 0.005=Asin(200*0.01) 0.005=A(0.0348) A=0.143 :( is this wrong?

34. Shayaan_Mustafa

there is no other way to do it. so it tried my best. and result is before you. :((

35. heena

i want to cry.. :"( )............ )............................ god if this kind of ques coming on exam i m gonna dead

36. Shayaan_Mustafa

37. Shayaan_Mustafa

i am sure it is right.

38. heena

1/9 i meantion it too

39. Shayaan_Mustafa

1/9 is equals to 0.1. so it is right. may be.

40. heena

yes u r rit u got it congo.........

41. Shayaan_Mustafa

congo?

42. heena

but in ur equation asinwt here t is time not time period

43. JamesJ

Heena. Let's try this one last time. Write out the complete question in your best English.

44. heena

lolz.. ok

45. hosein

46. heena

when an osicllator completes 100 oscilation then its amplitude reduced to 1/3 of its initial value of amplitude.what will be its amplitude if an osicllator completes 200 oscilation

47. JamesJ

This question is still very ambiguous. It means either * The time periods for the 100 and 200 oscillations are different and just a distraction. The amplitude is 3rd of what it is and that's the end of it. * We're talking about a pendulum and the period of oscillation changes. In which case we need to use the formula I wrote above * Something else.

48. Shayaan_Mustafa

i know. when i said it is true. it may be wrong. i just tried. although i am an electronics engineer not a theoritical physicist.

49. heena

guys had a idea leave it even i already wasted 30 mins in this ques better to leave this i ll ask my lecturer dont worry

50. Shayaan_Mustafa

yeah, good idea.

51. heena

thnQ for being here for help .. i always gave good ideas u knw gyan guru :P

52. hosein

why gave me medal i can't solve your ques

53. Shayaan_Mustafa

well i am going. good luck every one. take care.

54. heena

hey medal is not for only those who solve the ques but its for those too who atleast tries to solve it ok

55. heena

and i think u deserve as u given ur precious time to had a luk a my ques and tries it to solve as a help thnk you so much

56. hosein

this medal have not a value,i think however thanks for your attention sorry my english not well

57. heena

np i apreciate everyones work they did for helping others dats the main moto to give medals atleast people help others for medals.. and dnt think u dont solve dis medal is for ur work out in this ques ok..