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## Homework Statement

Consider an isolated system comprising two particles of masses m1 and m2, whose position vectors, in an inertial frame, are x1 and x2 and whose velocity vectors are v1 and v2. The interaction of the particles may be described by an energy function

E = 1/2 m1v1^2 + 1/2 m2v2 ^2 + U(x1, x2).

(a) Suppose that U = −k/r2, where k is a positive constant. Use energy conservation to determine the forces acting between the particles.

## Homework Equations

E = 1/2 m1v1^2 + 1/2 m2v2 ^2 + U(x1, x2). (1)

U = −k/r2, (2)

## The Attempt at a Solution

substituting U = −k/r2 into (1) gives

E = 1/2 m1v1^2 + 1/2 m2v2 ^2 −k/r2

then dont know what to do to determine the forces ,

i would think that gravtional forces are acting between the particles.