# Gravity and orbits

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#1
This is question F6.2 from Isaac Physics.

Calculate the orbital time period in years for a planet going round the Sun in an orbit of radius twice that of Earth.
Mass of Earth = 5.98×10^24kg
Seconds per year: 3.156×10^7

In question 1, I had to calculate the mass of the sun which I derived and used the equation (w^2 x r^3)/G = M and got 2.01e30 kg which was correct.

I have tried using the same equation but rearranging it for omega to then calculate the time period from this but I get a value of (24.85 s) 7.87e-7 years which is obviously wrong?
TIA
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#2
(Original post by Ktweed)
This is question F6.2 from Isaac Physics.

Calculate the orbital time period in years for a planet going round the Sun in an orbit of radius twice that of Earth.
Mass of Earth = 5.98×10^24kg
Seconds per year: 3.156×10^7

In question 1, I had to calculate the mass of the sun which I derived and used the equation (w^2 x r^3)/G = M and got 2.01e30 kg which was correct.

I have tried using the same equation but rearranging it for omega to then calculate the time period from this but I get a value of (24.85 s) 7.87e-7 years which is obviously wrong?
TIA
I have now correctly worked out this question using Keplers 3rd law to get T=2.83 years
0
3 years ago
#3
(Original post by Ktweed)
This is question F6.2 from Isaac Physics.

Calculate the orbital time period in years for a planet going round the Sun in an orbit of radius twice that of Earth.
Mass of Earth = 5.98×10^24kg
Seconds per year: 3.156×10^7

In question 1, I had to calculate the mass of the sun which I derived and used the equation (w^2 x r^3)/G = M and got 2.01e30 kg which was correct.

I have tried using the same equation but rearranging it for omega to then calculate the time period from this but I get a value of (24.85 s) 7.87e-7 years which is obviously wrong?
TIA
You don't need a lot of unit conversion for this type of question
it's asking for a ratio of periods (1 year is of course one orbital period of the sun for an object at one AU) and giving you a ratio of distances

you should be able to get it with just T2=r3
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