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![[Post New]](/templates/default/images/icon_minipost_new.gif) 14 Jul 2007 00:14:58 IST
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the mistake is in the line:
"also force reqd. to move A => (2m + m)(u/2)g + umg"
YOU MUST NOT INCLUDE THE "m" in the expression
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14 Jul 2007 01:03:45 IST
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the whole thing is out of order actually..
how can you calculate friction and stuff when there is no force applied?? how can a body start moving at a uniform velocity on its own? and if it was moving like that.. no friction will act on it.
ur concept was okay but there is one mistake, u want to consider a motion in which only friction makes the body move.. which is not possible.. friction opposes motion.. doesn't start it!
the ques is wrong!
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Sure i am that this day we are the masters of our fate, that the task set before us is not above our strengths; that its pangs and toils are not beyond our endurance. As long as we have faith in our own cause and an unconquerable will to win, victory will not be denied us.
- Winston Churchill |
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14 Jul 2007 07:45:31 IST
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hey ramyani wen both blocks are given a gentle push towards right,the frictional force on the upper block acts left and not right.. let f1 be frictioanl force on upper block.it is towards left -  (mg) = ma1 (force is in opp direction) a1 = - g f1 acts towards right for the lower block of mass 2m f2 due to ground acts leftwards (mg) - (m+2m)g/2 = 2ma2 a2 = (g)/2 - (3g)4 = a2 a1 - a2 = - g -- g/2 +3 g/4 =--3 g/2 +3 g/4 = - 3 g/4 3 g/4 in opp direction rate me if im rite
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kaushik krishna .R
bits pilani
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14 Jul 2007 07:47:33 IST
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suppose there is no friction between the bodies ,the lower block will slow down due to friction due to ground and the upper block will continue to move right. since there is friction the upper body also starts decelrating
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kaushik krishna .R
bits pilani
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14 Jul 2007 07:49:05 IST
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hey biki hav u interchanged the values of coeff . of friction
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kaushik krishna .R
bits pilani
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14 Jul 2007 08:56:08 IST
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do according to co-ordinate system.and the accl of a wrt b will be towards right n not left.hence it is positive
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14 Jul 2007 10:31:39 IST
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@ swaty...
you r mistaken ....
read your nudge book
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salman khan |
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14 Jul 2007 10:35:02 IST
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THE ANSWER 3ug/4 TOWARDS LEFT is very correct.
only pottermania could take it out...
but MR. POTTERMANIA...
your statement ma1 = - umg
implies ma1 + umg = 0........(HOW WILL YOU EXPLAIN THIS ???)
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salman khan |
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14 Jul 2007 10:37:27 IST
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WHEN A BODY MOVES WITH CONSTANT VELOCITY WE WRITE
FORCE IN A DIRECTION = FORCE IN THE OTHER DIRECTION
AND NOT
FORCE IN A DIRECTION = - (FORCE IN THE OTHER DIRECTION)
THEN WHY
ma1 = - umg ?????
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salman khan |
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14 Jul 2007 11:58:36 IST
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are you trying to tell me that friction is going to act without any force applied to the body??
how is the body given a velocity without applying any force??
plz explain me that.. i'll be grateful
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Sure i am that this day we are the masters of our fate, that the task set before us is not above our strengths; that its pangs and toils are not beyond our endurance. As long as we have faith in our own cause and an unconquerable will to win, victory will not be denied us.
- Winston Churchill |
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14 Jul 2007 13:50:55 IST
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pottert has done it in the other way.if not,can u tell me where m i going wrong?
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14 Jul 2007 20:59:48 IST
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OKAY I AGREE WITH ALL>>>>
but tell me how is the accl^n towards left....
@ pottermania
WHEN A BODY MOVES WITH CONSTANT VELOCITY WE WRITE
FORCE IN A DIRECTION = FORCE IN THE OTHER DIRECTION
AND NOT
FORCE IN A DIRECTION = - (FORCE IN THE OTHER DIRECTION)
THEN WHY
ma1 = - umg ?????
@ all
why leftward accl^n ?????
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salman khan |
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14 Jul 2007 21:09:05 IST
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biki the body will start 2 decelerate. though it is moving 2 the right friction is acting towards right it is decelerating due 2 friction thats y a -ive sign
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kaushik krishna .R
bits pilani
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14 Jul 2007 21:14:40 IST
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there is no force towards right u can ignore d force which causes d vel. only friction causes the decelation and it is 2ward left and thats y - mg = ma1 |
kaushik krishna .R
bits pilani
mech engg |
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