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![[Post New]](/templates/default/images/icon_minipost_new.gif) 17 Mar 2008 15:17:24 IST
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firsltly u havent written whether there is friction bw block and the wedge or not....
secondly, if friction is present and block is at rest wid respect to wedge, then work done by frictional force is 0.....
becoz....ncos theta = mg.....nsin theta=ma....due 2 this acceleration speed of block is v.....
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quote by swami vivekananda ji -In a day, when u don't come across any problem- u can be sure that u are traveling in a wrong path.... |
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17 Mar 2008 15:28:06 IST
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i can understand tarun's doubts but tarun u can apply work-energy theorem here  KE = Work by friction but there's no change in KE of the block as it continues to move with velocity v with respect to a stationary observer hence KE is =0 = Work by friction. U may also check it this way: change in total energy of block is = Work done by non conservative force which is friction in this case there's no change in potential or kinetic energy of block hence work done is 0
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I WAS BORN INTELLIGENT!!!!!!!
EDUCATION RUINED ME
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17 Mar 2008 16:12:24 IST
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@little brother.....friction is there
@someykathait............man in w-energy theorm u got to include work by normal reaction to.....see the figure...then only it will be zero...
i stick to my answer supposing friction does no work.... see the fbd i hav made...
work by (N sin theta) = change in kinetic energy.
.............by work energy theorem and as f cos theta does no work(supposing)....
here u see that there is a change in kinetic energy of the block as N sin theta does work..
frictional work is needed to cancel it
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17 Mar 2008 16:17:33 IST
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hey i think you got confused friction is used to oppose relative motion i hope u understand when there is no realtion between the block and wedge the frictional force betwwen the block and wedge does not do any work but the force of friction between the wedge and ground if it was there would have done work understood!!!
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17 Mar 2008 16:18:07 IST
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what about my second reason???
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I WAS BORN INTELLIGENT!!!!!!!
EDUCATION RUINED ME
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17 Mar 2008 16:19:00 IST
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ase toh u will say that..... Nsin (theta).......too did no work because it is at rest,,,,,,,,,,
THE NET WORK DONE BY FRICTION AND GRAVITY(NORMAL REACTION) IS ZERO AND THEREFORE THERE IS NO CHANGE IN KINETIC ENERGY....
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17 Mar 2008 16:21:09 IST
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OK HANG ON.......DO YOU AGREE THAT N sin theta DOES WORK......TELL ME FIRST
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17 Mar 2008 16:23:39 IST
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no!! idon't think so
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17 Mar 2008 16:28:45 IST
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.......I THINK IT DOES....
YAAR IF YOU LOOK AT IT..IT IS MOVING WITH A VELOCITY OF V ...SO DISPLACEMENT IS THERE FROM THE GROUND VIEW...
AND SOME FORCE MUST BE CARRYING IT THERE...ISN`T IT...IT CAN NOT FLY OFF...SO THE FORCE N SIN THETA IS CARRING IT THERE..BY DOING WORK..
NOW IF IT IS DOING WORK..THEN BY WORK ENERGY THEOREM THERE IS A CHANGE IN KINETIC ENERGY BUT IT IS NOT..
TO HAVE THIS FRICTION IS DOING EQUAL AND OPPOSITE WORK HOPE YOU GET IT ...
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17 Mar 2008 16:30:04 IST
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is question ke author ko to bolo what's the answer dude?????
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I WAS BORN INTELLIGENT!!!!!!!
EDUCATION RUINED ME
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17 Mar 2008 16:40:23 IST
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ok!! then do u agree that if the wedge is assumed to be at rest then also the fbd of the wedge and the block would remain same as it is now. In this case(v=0) the work by friction is 0 u may agree this. So what's the difference when wedge is moving with constant velocity (acc=0).
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I WAS BORN INTELLIGENT!!!!!!!
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17 Mar 2008 16:43:53 IST
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thats all dependent on the frame man..
that is the confusion of frames
remember one point
WORK IS FRAME DEPENDENT
there are things like these in physics which are far from your common experiences but good effort dude ...i salute you
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