From universal law of gravitation, gravitational force exerted on a body of mass m by another body of mass M is F=GMmx2
where x is the distance between the centres of both the objects.
So, work done by gravitational force in bringing the object of mass m from infinity to a distance r from the centre of body of mass M is W=∫r∞→F(x).→dx
=∫r∞GMmx2ˆx.→dx
(where ˆx is the unit vector in the direction in which the body of mass M is attracting the body of mass m, i.e. the direction of →dx which results the angle between both vectors 0) =∫r∞GMmx2dx cos0
=−GMm(1r−1∞)
=−GMmr
Now, we know that W=−(∆U)
−GMmr=−(Ur−U∞)
−GMmr=(U∞−Ur)
Since, Zero of potential energy is at infinity by convention, so U∞ = 0 −GMmr=−Ur
GMmr=Ur
I get potential energy at a distance r as positive, then why is it that gravitational potential energy is −GMmr
What is wrong in my derivation?
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