Calculate angular momentum of a planet only velocities and radii known

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Homework Statement


a planet of mass m orbits a star. The Velocity at point A = 10^4 m/s the Radius at point A = 10^7, Vb = (10^4)/3, Rb = 3*10^7
Numerically calculate the angular momentum!

Homework Equations



The main question is how would you calculate the mass?

The Attempt at a Solution


L = rmv sintheta or L = IW but you need the mass.
E =1/2 *mv^2 - mMG/r but you need the mass for this as well. I also tried finding the value of mass by finding it in terms of one of the equations but you need more unknowns
 
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Answers and Replies

  • #2
785
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Homework Statement


a planet of mass m orbits a star. The Velocity at point A = 10^4 m/s the Radius at point A = 10^7, Vb = (10^4)/3, Rb = 3*10^7
Numerically calculate the angular momentum!

Homework Equations



The main question is how would you calculate the mass?

The Attempt at a Solution


L = rmv sintheta or L = IW but you need the mass.
E =1/2 *mv^2 - mMG/r but you need the mass for this as well. I also tried finding the value of mass by finding it in terms of one of the equations but you need more unknowns
Angular momentum at a, right? Apply law of conservation of angular momentum. You will notice that mass cancels out. :smile:

BTW, welcome to PF !!
 

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