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![[Post New]](/templates/default/images/icon_minipost_new.gif) 11 Apr 2008 14:28:24 IST
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plz help me.
Q. A solid body starts rotating abt a stationary axis with an angular acceleration  = ( 2.0 * 10-2 ) t rad / sec2 , where t is in secs. How soon after the beginning of rotatio will the total accln vector of an arbitrary point of the body form an angle theta = 60 with its velocity vector ?
( D C Pandey, vol II , p,17)
Detailed expln plz. I m very weak in this chapter.
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it is not important where u stand, but in which direction u are moving |
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11 Apr 2008 23:44:52 IST
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Plz someone help !!
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it is not important where u stand, but in which direction u are moving |
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12 Apr 2008 00:59:05 IST
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acceleration in tangential direction=direction of velocity vector
At=0.02
and total A=[ ] at2+ar2
also ar/at=tan 60=root 3
w2r=root 3*0.02
so we can find w
now w=0.02t
so t=50 w
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" Always remember money isn't everything but make sure you have made a lot of it before talking such nonsense!"
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12 Apr 2008 10:43:49 IST
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= 2*10-2 t
=d / dt
hence
d = 2*10-2 tdt
on integrating
= 10-2 t2
a tangential =  r = 2*10-2 t
a centripetal = 2r = 10-4 t4
also
tan 60 = 3 = a centripetal / a tangential
= t3 / (2 * 102 )
hence
t3 = 2* 3*102
 346.4
or
t 7 seconds
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Impossible To be Impossible is Impossible |
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12 Apr 2008 11:18:00 IST
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if it is 60degrees the ans is 2pie/3 secs
if 60rads den 120 secs
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>>sugeet->
--catalysingsuccess |
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12 Apr 2008 17:00:48 IST
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@ sugeet
how ??
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Impossible To be Impossible is Impossible |
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12 Apr 2008 18:21:40 IST
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The answer is 7 secs.
total accln vector form an angle theta = 60 with its velocity vector
tan 60 = 3 = a centripetal / a tangential
= t3 / (2 * 102 )
not clear !!
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12 Apr 2008 18:25:03 IST
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@Ramyani:
Understand that the direction of tangential acceleration and tangential velocity are the same. Hence, the required angle is the angle that the total acceleration vector makes with the tangential acceleration vector.
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Will nip in at times to solve problems :)
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12 Apr 2008 18:26:21 IST
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if what karthik has explained does not bring clarity still
i'll post a diagram if u want .
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Impossible To be Impossible is Impossible |
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12 Apr 2008 18:29:49 IST
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ok ! yes !
the total acceleration vector--where ?
caln was for centriptal and
tan 60 = 3 = a centripetal / a tangential
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12 Apr 2008 18:31:53 IST
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See.....
Atotal = A2centripetal+A2radial
Now, Acentripetal = Fy
Aradial = Fx
We know that the angle made by the resultant with Fx is tan-1(Fy/Fx)
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Will nip in at times to solve problems :)
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12 Apr 2008 18:33:44 IST
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oops !!!
thank u !!
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it is not important where u stand, but in which direction u are moving |
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13 Apr 2008 00:07:13 IST
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anchit what integrating limiys u took why
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