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![[Post New]](/templates/default/images/icon_minipost_new.gif) 23 Nov 2007 19:13:35 IST
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5 Salutes to one who gets it right.
(No Diagram given)
Q)A sledge filled with sand slides down without friction down
a 300 slope.Sand leakes out through a hole in the sledge at
a rate of 2 Kg per second.If the Sledge starts from rest
from the top of inclineand if total initial mass of Sledge is
40 Kg, How long does it take to go down 120 metre in the
plane?
Everyone who gives a good effort will be rated.
Solution will be posted tomorrow by 4.00 pm.
ALL THE BEST.....WISH YOU ALL GOOD LUCK.
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Always available for help !
But Remember Don't hesitate to ask a good Question but
Be damn serious for Questioning a weak one.
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23 Nov 2007 19:30:28 IST
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Is it 1.1 seconds?
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Will nip in at times to solve problems :)
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23 Nov 2007 19:34:23 IST
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i may go wrong but i think when a body goes down an inclined plane without friction, its acceleration does not depend on its mass
so its acc should be gsin30
so 120=1/2gsin30t^2
but \\
this is a jee problem, may not be so easy,
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- Edward Everett Hale
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23 Nov 2007 19:37:33 IST
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I'm getting 1.105 and 6.9 seconds!!. The third value is negative
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23 Nov 2007 19:42:20 IST
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Well,Not close but atleast trying....... :)
Try keep trying..... 
The answer is:
38.8 sec.
Cheers!!!!!!!!@@@!!!!!!!!!
It took me more then 45 mins to crack it when I did it.
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Always available for help !
But Remember Don't hesitate to ask a good Question but
Be damn serious for Questioning a weak one.
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23 Nov 2007 19:45:40 IST
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It took me more then 45 mins to crack it when I did it.
Anyways Best of Luck to all.
Cheers!!!!!!!!@@@!!!!!!!!!
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Always available for help !
But Remember Don't hesitate to ask a good Question but
Be damn serious for Questioning a weak one.
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23 Nov 2007 19:45:59 IST
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blunder by me! trying again...
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I am only one,
But still I am one.
I cannot do everything,
But still I can do something;
And because I cannot do everything
I will not refuse to do the something that I can do.
- Edward Everett Hale
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23 Nov 2007 19:47:39 IST
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Mass of sledge is not given? If sledge is assumed to be massless, then t=38.8 gives negative mass
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Will nip in at times to solve problems :)
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23 Nov 2007 19:50:02 IST
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Hint:Make assumptions say "m" is the mass" and take some
"dt" time and then use some Brains !!!!!!!!!
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Always available for help !
But Remember Don't hesitate to ask a good Question but
Be damn serious for Questioning a weak one.
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23 Nov 2007 19:52:02 IST
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Bleh... stupid mistake by me... I think i got the logic. Trying to find out the mass of the sledge now
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23 Nov 2007 20:11:57 IST
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If the sledge mass is found... the problem is over. But finding it is the whole problem :(
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23 Nov 2007 20:12:19 IST
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Still trying.... dont post the solution now
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23 Nov 2007 21:00:13 IST
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force = (dm/dt)v + (dv/dt)m the sledge suffers a vertical displacement of 120sin30 = 60m So let us find the velocity of the body after t sec while it covers 120m. initial velocity = 0, initial mass = 40kg final velocity = v , final mass = (40 - 2t)kg using energy conservation.... 40x10x60 + 0 = (1/2)(40-2t)v2 or v = 40  30 / (40 - 2t) So let us find the force acting on the sledge at the final position. F = (dm/dt)v + (dv/dt)m = {2x40 30 / (40 - 2t)} + {10sin30 x (40 - 2t)} N and force acting on the body initially = F' = 40 x 10sin30 = 200 N initial accl^n = 200/40 = 5 m/s^2 = a' final accl^n =[ {2 x 40 30 / (40 - 2t)} + {10sin30 x (40 - 2t)} ] / (40 - 2t) = a here i am having a problem... can i take avg. accl^n as ( a + a' ) / 2 = A (say) and use the equation 120 = (1/2)At2 to obtain an equ^n in t and solve for t ..??
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salman khan |
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23 Nov 2007 21:01:01 IST
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i don't think i am correct
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salman khan |
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