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Blazing goIITian

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17 Mar 2010 19:43:50 IST

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The K.E needed to project a body of mass m from the earth's surface to infinity is {explain}......

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The K.E needed to project a body of mass m from the earth's surface to infinity is {explain}...........a) mgR b) 2mgR c)1/2 mgR

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shashank agarwal

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17 Mar 2010 21:46:25 IST

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(a) is correct

mardav, NIT-B civil engineering.

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17 Mar 2010 21:46:54 IST

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yes.a) is correct

Aakash Anuj

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18 Mar 2010 17:49:05 IST

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when the body is at infinity,, the sum of the KE and PE is zero. hence the total initial energy should also bezero. Conserving ergy, GMm/R = 1/2mv^2 we get v=root (2gR) which is independent of the mass of the body. hence option A is correct.

edison

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18 Mar 2010 17:55:23 IST

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The KE needed to project the body of mass 'm' from the earth's surface to infinity is equal to the Graviational Potential Energy (PE) of mass and earth system,

i.e. KE = PE

or KE = GM_em / R

But GM/ R² = g

or GM/R = gR

Thus KE = mgR

Hence correct option is (A)

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