Conservation of Angular Momentum in Molecular Cloud Collapse

AI Thread Summary
The discussion revolves around calculating the new rotation period of a molecular cloud as it collapses to the size of the Sun while conserving angular momentum. The initial parameters include the cloud's size of 0.2 light years and its rotation period of 1.4 × 10^7 years. Participants debate whether to use the mass of the Sun in calculations, noting that the mass remains constant during the collapse. Key equations involve angular momentum, expressed as l = mvr, and the challenge lies in determining the cloud's angular momentum before collapse. The conversation highlights the importance of understanding the initial conditions and assumptions regarding the cloud's shape during the calculation.
Meganwright
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Homework Statement



A molecular cloud 0.2 light years across rotates once every 1.4 ×107 years. If it were to collapse to the size of our Sun, how long would it take to rotate once if it conserved angular momentum given by mvr, where m is mass, v is the circular rotation speed and r is the radius. Is this reasonable in this case?

Homework Equations



l=mvr

The Attempt at a Solution


the suns rotation is approx 26.8 days
the radius i worked out to be 0.1 x 9.4605284 × 10^15 metres = 9.4605284 x 10^14 metres
rotation= 1.4 x 10 ^7 years
do i also use the mass of the sun?
in which case m=1.99 x 10^30 kg?

then sub into
l=mvr ?
 
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You don't care about the mass or the rotation rate of the Sun. On collapse, the mass will be the same as the original cloud.
What is the angular momentum of the cloud before collapse? (I don't know whether you're supposed to assume a ball or a disc.)
 

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