What is the work done on a comet orbiting a star?

AI Thread Summary
In the discussion about the work done on a comet orbiting a star, it is clarified that work is defined as force multiplied by displacement, with the force needing to align with the direction of motion. While a circular orbit results in no work being done due to the perpendicular relationship between force and displacement, a comet's elliptical orbit complicates this. At points A and D, where potential and kinetic energy are at extremes, the work done is indeed zero. However, at other points in the orbit, the gravitational force has a component that aligns with the comet's momentum, indicating that work is done. This understanding highlights the complexities of gravitational interactions in non-circular orbits.
ccarit3007
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If a comet is orbiting a star is there any work done? I understand that work is force * displacement, but the force must be in the direction of motion. In the case of a comet and star the star exerts a gravitational force on the comet, but this force is not in the direction of the motion of the star (as the motion is circular). Is this the correct logic? For the question in the image shown I understand that potential energy would be greatest at A and kinetic would be greatest at D, but I still am stumped on the work side of things.
 

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You are correct that if the orbit is circular then the force and the displacement are perpendicular, so no work is done. However, a comet's orbit is not circular...
 
phyzguy said:
You are correct that if the orbit is circular then the force and the displacement are perpendicular, so no work is done. However, a comet's orbit is not circular...
Yes, I understand that. So when you are not at point A or point D the force will not be perpendicular to the velocity (and momentum). I'm not sure exactly what this means/where I go from there? I'm guessing that means the work at A & D is 0?
 
ccarit3007 said:
Yes, I understand that. So when you are not at point A or point D the force will not be perpendicular to the velocity (and momentum). I'm not sure exactly what this means/where I go from there? I'm guessing that means the work at A & D is 0?
Ah thinking about this again, the net force which would be directed towards the star would have a component that is in the direction of the momentum. Is this correct?
 
ccarit3007 said:
Ah thinking about this again, the net force which would be directed towards the star would have a component that is in the direction of the momentum. Is this correct?

It would have a component of the force directed in the direction of motion, yes.
 

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