Conceptual problem: Finding gravitational KE

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SUMMARY

To find the kinetic energy (KE) of an orbiting body, one can use either the formula 1/2mv² or 1/2Gm₁m₂/r, depending on the context of the problem. In a circular orbit, the gravitational force acts as the centripetal force, leading to the relationship mv²/r = GMm/r². Consequently, the kinetic energy can be expressed as KE = 0.5GMm/r, which is derived from the gravitational potential energy (GPE) equation. The total energy of an orbiting body is represented as KE + GPE = -0.5GMm/r.

PREREQUISITES
  • Understanding of Newton's laws of motion
  • Familiarity with gravitational force and potential energy
  • Knowledge of circular motion dynamics
  • Basic algebra and manipulation of equations
NEXT STEPS
  • Study the derivation of gravitational potential energy in orbital mechanics
  • Learn about the conservation of mechanical energy in orbital systems
  • Explore the differences between kinetic energy and gravitational potential energy
  • Investigate the implications of varying orbital radii on kinetic energy
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Students studying physics, particularly those focusing on mechanics and gravitational systems, as well as educators seeking to clarify concepts related to orbital motion and energy conservation.

grantP
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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

 
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Hi grantP,

grantP said:

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.
 
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
 

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