# Universal Gravitation

kim3648
Neutron stars are extremely dense objects that are formed from the remnants of supernova explosions. Many rotate very rapidly. Suppose that the mass of a certain spherical neutron star is twice the mass of the Sun and its radius is 5.0 km. Determine the greatest possible angular speed it can have so that the matter at the surface of the star on its equator is just held in orbit by the gravitational force.

First I would find escape velocity
https://www.physicsforums.com/latex_images/11/112728-0.png [Broken]
And using that velocity as the tangent I could find the angular velocity? Is that a correct assumption?

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dwintz02
Hmm, this problem is a little tricky in disguise. If matter at the equator is JUST held on my gravity, that means the object is ALMOST weightless. Use a force balance and set that equal to m*centripedal acceleration and then ask yourself what it means to be weightless. Where does that get you?

kim3648
I think you have my question confused with that of the person below me !

dwintz02
That's interesting. I think you have your question confused with another one! No, but really...you can do your problem either way. It's just easier the way I said in my opinion.

Homework Helper
First I would find escape velocity
https://www.physicsforums.com/latex_images/11/112728-0.png [Broken]
And using that velocity as the tangent I could find the angular velocity? Is that a correct assumption?

It's not necessary here to find escape velo. The force due to gravity should be equal to the centrifugal force at the equator. The same as dwintz02 said.

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Homework Helper
That's interesting. I think you have your question confused with another one! No, but really...you can do your problem either way. It's just easier the way I said in my opinion.

He can't do it using escape velocity.