# Energy due to central force

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A body of mass 2 kg is moving under the influence of a central force whose potential energy is given by U (r) = 2r$^3$ Joule. If the body is moving in a circular orbit of 5m, we have to then find its energy.

I tried as
$$F(r)=-\frac{dU}{dx}=-6r^2=mv^2/r$$
$$F(5)=150=mv^2/r$$
$$(1/2)mv^2=375J$$

But the energy given as 625J

You have found KE but what about PE?
You mean PE = 2(5)$^3$=250