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27 Apr 2009 20:28:28 IST
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another 1...aieee-09

If x, v and a denote the displacement, the velocity and the acceleration of a particle executing simple harmonic motion of time period T, then, which of the following does not change with time ?

(1) aT + 2

pv             (2)aT/v2T2 + 4p2v2            (4)aT/x

(3) a


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Comments (45)

27 Apr 2009 20:31:42 IST
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sorry the options are...1) aT+2piev .....2)aT/v....3)a^2T^2+4(pie)^2v^2.....4)aT/x
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Blazing goIITian

Joined: 13 Aug 2008
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27 Apr 2009 20:33:18 IST
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Answer is aT/x

 

juz take an example .... like x = M sin (wt + kx)

 

this exectutes SHM u know and v = dx/dt, T = 2pi/(w) doesnt vary wid time

and a = dv/dt

substitute this, u get aT/x doesnt change wid time :)

 

 


Blazing goIITian

Joined: 9 Oct 2008
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27 Apr 2009 22:58:28 IST
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Answer is d...

I did it like this;
aT/x ==> (-aw2sinwt)/(a sinwt) * (2?/w)... which will give: -a2?/w... which is independent of change in time with any respect...
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27 Apr 2009 23:00:14 IST
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hi guys ..answer is d) aT/x ...the point here is simple...T is constant ,,and a=kx ,so a/x also constant. enjoy!


Blazing goIITian

Joined: 9 Oct 2008
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27 Apr 2009 23:01:48 IST
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Thats' what we are answering nugo
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Blazing goIITian

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27 Apr 2009 23:03:12 IST
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i neva said u r wrong or only i m rite....(i said to enjoy) ...i was just givng wat i thot there.....many methods are there to solve a problem of which all can be correct.


Blazing goIITian

Joined: 9 Oct 2008
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27 Apr 2009 23:25:25 IST
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yupi.. neither I'm contradicting... cheers

Hot goIITian

Joined: 26 Jul 2007
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28 Apr 2009 05:54:54 IST
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there are 2 options correct...... even the a2 T2 + 4(pi)2 v2    is correct...

a=-ω2x

T=2(pi)/ω

....v=

so,a2T2 is ω4x2 4 (pi)2 ω-2 ..............and ........4(pi)22(A2 - x2))....so...if u sum them up and simplify,the term contaning x gets cancelled and u get,

........4(pi)2 ω2   A2 ..........WHICH IS CONSTANT!!!!!!.....

28 Apr 2009 09:59:42 IST
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ya kartik is right....we have two correct answers...c) and d)
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28 Apr 2009 10:02:34 IST
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ya i also marked it option 2 bcoz after calculations i found it coming a constant......
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Blazing goIITian

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28 Apr 2009 10:05:47 IST
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these aieee ques are killing students this time........i dont think any reason is there for my ans to be wrong.
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28 Apr 2009 11:22:36 IST
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@lalit,karthik....

option c may not always be true

in the case of damped oscillation, A is an exponentially decaying function of time, isnt it?

whereas option d is true irrespective of the amplitude of oscillation, since it is the hallmark of any simple harmonic  oscillation,

damped or otherwise, so it is the MOST appropriate, although people may argue that the question isnt specific......

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28 Apr 2009 11:28:41 IST
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people don't know how to question nowadyas.they willingly gave the answer an option as aT/x which most of us(even I) marked but they are canceling it on the basis that a/x isn't defined at x=0. but does the question asks about the domain or range of x. i mean agar defined nahi hai par jaaha pein define hai waha to constant hai.matlabF(X)={ x=9; x belongs to real-{1}} isn't constant......................argument on the basis of damping might not be justified as damping is not in syllabus...........they should have asked which one of the follwoing is always defined and constant.

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Blazing goIITian

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28 Apr 2009 11:39:39 IST
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well obviously one tends to assume that the question is related to wherever the function is defined and

3 may be rejected on the basis of damping........4 makes a lot more physical sense to me and i did think of situation at x=0 during the

exam but i like several others assumed the above.................vague question.......

it's a physics question. after all...

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Blazing goIITian

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28 Apr 2009 11:57:11 IST
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I marked 4 actually I was too confused in it. there are few more contro. questions. I don't know how those people set the paper...it was full of such confusing ones.
pushkar limaye's Avatar

Cool goIITian

Joined: 4 Jun 2007
Posts: 44
28 Apr 2009 12:01:16 IST
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at/x is wrong as we r not given that x is disp. from mean position.e.g.if eqn is X=10+5SIN(WT),then at/x is not cons.

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Blazing goIITian

Joined: 27 Dec 2007
Posts: 689
28 Apr 2009 12:05:53 IST
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uh no.....i can always shift the origin, cant i?

dreamer lalit iitr's Avatar

Blazing goIITian

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28 Apr 2009 12:15:02 IST
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yaar even iit does not take damping into account and i wud never had thought in my weirdiest of my deams that aieee can ask damping related ques.....yaar ye to wahi baat ho gayi jab koi aur reason nahi mila to damping reason de do
28 Apr 2009 12:21:22 IST
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but the answer key says that 3 and 4 both r correct



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