Conceptual problem: Finding gravitational KE

[grantP]

Homework Statement

to find KE of an orbiting body, do I use 1/2mv^2 or 1/2Gm1m2/r??

Homework Equations

The Attempt at a Solution

 

[alphysicist]

Hi grantP,

Homework Statement

to find KE of an orbiting body, do I use 1/2mv^2 or 1/2Gm1m2/r??

If it's a circular orbit (for example) then it would just depend on which is more convenient for the problem.

 

[unscientific]

For an orbiting body, gravitational force provides for the centripetal force:

mv²/r = GMm/r²


0.5mv² = 0.5GMm/r


Just to digress abit, so the total energy an orbiting body with distance r away from the centre of the planet is:

KE + GPE = 0.5GMm/r + (-GMm/r)

= -0.5GMm/r