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![[Post New]](/templates/default/images/icon_minipost_new.gif) 11 Sep 2007 02:49:46 IST
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Q. ! person says that P.E. of a particular book kept in an almirah is 20 J and the other says it is 30 J .Is 1 of them necessarily wrong ?
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it is not important where u stand, but in which direction u are moving |
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11 Sep 2007 11:35:15 IST
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Nope!!
The potential enegry of an object is calculated from a referance where the GPE is ACCEPTED zero.
There is no hard and fast rule regarding the choice of referance. After all the change in potential energy is important not the potential energy itself. So they both are correct.
Hope u r clear.....
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"If you win, you shall not have to explain and if you lose, you wont be there to explain"
~ Adolph Hitler |
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11 Sep 2007 12:33:21 IST
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I think u r right. But is it so trivial ? HCV alwas has some tricks under the cuff.
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it is not important where u stand, but in which direction u are moving |
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11 Sep 2007 17:02:15 IST
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My above argument is correct only when the value of g is constant throughout the system (In this car room or whatever)
You can assume the whole almarih and the book as a 'system'. Now this system is in the Gravitational field of earth such that the value of gravitational accelaration is g. Now if g is constant with height in the system then you can consider any referance. But if g varies significantly then the above argument fails and you have to consider the absolute GPE, i.e. by taking g = Rt (GMe/Re).
But here you can safely asssume that g won't vary significantly as our system has very small dimensions.......
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