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    Name:  Screenshot_2016-03-11-12-13-59.png
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Size:  381.5 KB hi is there anyone out there who could help me understand why they are proportional and how to solve this question?

    Before I lose my sanity lol
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    (Original post by physicsstudent27)
    Name:  Screenshot_2016-03-11-12-13-59.png
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Size:  381.5 KB hi is there anyone out there who could help me understand why they are proportional and how to solve this question?

    Before I lose my sanity lol
    What does Kepler's third law state?
    Think of the summary equation.
    Rearrange, and prove your question!
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    (Original post by physicsstudent27)
    Name:  Screenshot_2016-03-11-12-13-59.png
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Size:  381.5 KB hi is there anyone out there who could help me understand why they are proportional and how to solve this question?

    Before I lose my sanity lol
    Falls out of Newton's gravitational law and formula for centripetal acceleration.
    And you have to relate T to the velocity.
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    (Original post by physicsstudent27)
    Name:  Screenshot_2016-03-11-12-13-59.png
Views: 106
Size:  381.5 KB hi is there anyone out there who could help me understand why they are proportional and how to solve this question?

    Before I lose my sanity lol
    Use circular motion formulae with gravitational attraction to derive Kepler's equation that'll show that T^2 = kr^3.

    Remember what \omega = \frac{2\pi}{T}

    Edit: lol **** this nvm got ninjaed twice over :rofl:
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    (Original post by physicsstudent27)
    Name:  Screenshot_2016-03-11-12-13-59.png
Views: 106
Size:  381.5 KB hi is there anyone out there who could help me understand why they are proportional and how to solve this question?

    Before I lose my sanity lol
    Equate the gravitational force to the centripetal
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    (Original post by EricPiphany)
    Falls out of Newton's gravitational law and formula for centripetal acceleration.
    And you have to relate T to the velocity.
    Just use the form of centripetal force with omega
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    (Original post by samb1234)
    Equate the gravitational force to the centripetal
    The way you phrased this is a bit misleading, isn't it? The gravitational force provides the centripetal force, you don't equate the two.
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    (Original post by samb1234)
    Just use the form of centripetal force with omega
    velocity could mean 'angular velocity' too
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    (Original post by Zacken)
    The way you phrased this is a bit misleading, isn't it? The gravitational force provides the centripetal force, you don't equate the two.
    Yeah I guess the phrasing isn't the best tbh, but as you say since the gravitational force is the centripetal force that is essentially the method
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    hope this helps.
    its all I could remember from A level physics since starting my degree.
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    Thanks a lot guys I am pretty comfortable with the idea that when a object in circular orbit that the centripetal force is the resultant force. I am just not comfortable with the way the questions are worded or the idea of proportionality. Especially when they give me a quest like t1/r1 = t2/r2 work out blah blah something like that
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    Probably just need to practice... they do seem to love ratio/proportionality questions in astronomy papers.
 
 
 
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