we say that work done on a body in moving it from infinity to some point in gravitational field is equal to the -ive of the change in pot. energy when body is moving slowly i.e. with no k.e ok......now if body is moved from infinity to a particular point in gravitation field such that body possess some k.e( i.e moving with some velocity)......now tell me work done by the external force is and gravitational force is....i am little confused with this..plz explain with suitable example....ok....plz.....waiting
Well, when the body moves from infinity to some point in the space without any help of any external force(it can do so if you place it at the so-called infinity boundary and jiggle it a bit), the gravity does +ve work on it and its KE increases and this would be equal to -ve of change in gravitanional P.E = -(-GMm/R-0) = GMm/R. But when you move it using a force directed against the gravitational force, its KE gets decreased as the force does negative work on it, hence K.E = -P.E + Wexternal. It should be noted that in any case the W done by garvity remains the same no matter what bloody darn force acts on it W = -P.E. The work done by the force is K.E + P.E
Moderation Team
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K.E = -
