# Gravitational fields questions

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1. There is a graph that shows T^2 against r^3, the question askes it to calculate the planets mass, what do I do with the graph?

2. Question : All vector fields have an associated scalar potential. For this question assume earth has a radius of 6400km and a mass of 6x10^24 kg.

Given the gravitational potential Vg is 63 MJ kg^-1 at earths surface calculate Vg at an altitude equal to earths radius?

Calculate the gravitational potential energy of a 10kg ball at an altitude equal to three times earths radius?

Any one who can help me with how I work any of these out, thank you in advanced

2. Question : All vector fields have an associated scalar potential. For this question assume earth has a radius of 6400km and a mass of 6x10^24 kg.

Given the gravitational potential Vg is 63 MJ kg^-1 at earths surface calculate Vg at an altitude equal to earths radius?

Calculate the gravitational potential energy of a 10kg ball at an altitude equal to three times earths radius?

Any one who can help me with how I work any of these out, thank you in advanced

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(Original post by

1. There is a graph that shows T^2 against r^3, the question askes it to calculate the planets mass, what do I do with the graph?

......

Any one who can help me with how I work any of these out, thank you in advanced

**heathersmusical**)1. There is a graph that shows T^2 against r^3, the question askes it to calculate the planets mass, what do I do with the graph?

......

Any one who can help me with how I work any of these out, thank you in advanced

where G is the gravitational constant and M is the mass of the planet.

So you can find the mass of the planet by determining the gradient of the T^2 against r^3 graph. The gradient is

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(Original post by

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2. Question : All vector fields have an associated scalar potential. For this question assume earth has a radius of 6400km and a mass of 6x10^24 kg.

Given the gravitational potential Vg is 63 MJ kg^-1 at earths surface calculate Vg at an altitude equal to earths radius?

Calculate the gravitational potential energy of a 10kg ball at an altitude equal to three times earths radius?

Any one who can help me with how I work any of these out, thank you in advanced

**heathersmusical**)....

2. Question : All vector fields have an associated scalar potential. For this question assume earth has a radius of 6400km and a mass of 6x10^24 kg.

Given the gravitational potential Vg is 63 MJ kg^-1 at earths surface calculate Vg at an altitude equal to earths radius?

Calculate the gravitational potential energy of a 10kg ball at an altitude equal to three times earths radius?

Any one who can help me with how I work any of these out, thank you in advanced

https://www.s-cool.co.uk/a-level/phy...onal-potential

So the Vg at an altitude equal to earths radius is

where M_E is the mass of Earth and R_E is the radius of the Earth.

Note that there are at least 2 ways of doing this for this question. You should be familiar with them.

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Thank you so much !!

(Original post by

For Q2, you need to know that gravitational potential for a mass M is defined by

https://www.s-cool.co.uk/a-level/phy...onal-potential

So the Vg at an altitude equal to earths radius is

where M_E is the mass of Earth and R_E is the radius of the Earth.

Note that there are at least 2 ways of doing this for this question. You should be familiar with them.

**Eimmanuel**)For Q2, you need to know that gravitational potential for a mass M is defined by

https://www.s-cool.co.uk/a-level/phy...onal-potential

So the Vg at an altitude equal to earths radius is

where M_E is the mass of Earth and R_E is the radius of the Earth.

Note that there are at least 2 ways of doing this for this question. You should be familiar with them.

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