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![[Post New]](/templates/default/images/icon_minipost_new.gif) 28 Mar 2008 11:13:19 IST
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assertion&reasoning:
1.A:let us consider a case,in which we know the details of initial motion of system,then it is possible to know description of final motion,without knowing the details of forces which are changing the motion of the system
R:Fext=dP/dt
2.A:PE of a system is changing,it means configuration(means arrangement of different parts of sys wrt each other)changes
R:external conservative forces acting on system changes the configuration of system
true or false:
1.momentum of a non closed system can remain constant(non closed means mass not constant)
pls explain
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28 Mar 2008 11:16:59 IST
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Assertion is False
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28 Mar 2008 11:18:12 IST
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why
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28 Mar 2008 11:18:12 IST
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edit: 3)
true...if ext forces cancel out
initially this was 2nd but u put another q in between
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28 Mar 2008 11:19:02 IST
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but as per definition it shud be a closed system naa
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28 Mar 2008 11:20:12 IST
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1)
consider a car initial v=20m/s
after time t,if there was friction the vel wud have dec,if road was smooth same vel...
if he had stepped on the accelerator(ext force on the car) the car vel wud inc
so unless u no wat happens u cant decide on final motion
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28 Mar 2008 11:20:55 IST
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net force acting on the body as a function of time should be known to determine the final conditions.
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28 Mar 2008 11:21:09 IST
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closed system means : No external force @ all
open system can have 2 forces acting with net force=0
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28 Mar 2008 11:22:01 IST
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hoe cud that be an external force
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28 Mar 2008 11:23:47 IST
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which??
acceleration??
well u r ejecting fuel gases @ vel
so thrust on the car = dm/dt * vrel
But thts not the pt...
u can c tht u cant determine widout knowledge pf forces
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28 Mar 2008 11:24:25 IST
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1st is false becoz if u dont know the acceleration of body during the time inteval... we cannot predict the final states...
2nd : both assertion and reason are true... but reason is not corretct
3rd.... is true..... if work is not done by the xt force acting on it
i mean it can... not always remain constant
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size doesnt matter, brains do...
vignesh |
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28 Mar 2008 11:24:32 IST
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closed system means no mass exchange naa
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28 Mar 2008 11:27:16 IST
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mr.cool only the 3rd one is correct
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28 Mar 2008 11:31:05 IST
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edited the 3rd qn
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28 Mar 2008 11:34:45 IST
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edit
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