# Help understanding question

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#1
http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF

Q 4biii) I dont understand what the question means.

Thanks!
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6 years ago
#2
(Original post by Zenarthra)
http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF

Q 4biii) I dont understand what the question means.

Thanks!
It's asking for an explanation why the gravitational potential due to that of the sun does not need to be taken into account when calculating the minimum energy needed to move the spaceprobe from the earth to point X.
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#3
(Original post by uberteknik)
It's asking for an explanation why the gravitational potential due to that of the sun does not need to be taken into account when calculating the minimum energy needed to move the spaceprobe from the earth to point X.
Ahh ok thanks and hi!
Well would i be right in saying:
The gravitation potential due to the sun on the earth is given by V=-GM/r
As the distance from the sun to the earth is so great, the gravitational potential at earth due to the sun will be negligible.
Considering a very small number of V multiplied by the distance from earth to X, giving the extra work done due to the gravitational potential of the sun. This value is so insignificant than that of the work needed to move a space probe through dV of gravitational potential due to the earth, that it does not affect the minimum energy.

thanks.
0
6 years ago
#4
(Original post by Zenarthra)
Ahh ok thanks and hi!
Well would i be right in saying:
The gravitation potential due to the sun on the earth is given by V=-GM/r
As the distance from the sun to the earth is so great, the gravitational potential at earth due to the sun will be negligible.
Considering a very small number of V multiplied by the distance from earth to X, giving the extra work done due to the gravitational potential of the sun. This value is so insignificant than that of the work needed to move a space probe through dV of gravitational potential due to the earth, that it does not affect the minimum energy.

thanks.
Not quite.

Think of the F = GmM/r2 relationship and the gravitational field in the vicinity of the earth due to the sun. It does not change significantly because the distance change from the earth to the moon is around 0.3% of the distance to the sun. Hence the force difference at that distance changes by an insignificant amount.
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#5
(Original post by uberteknik)
Not quite.

Think of the F = GmM/r2 relationship and that the because the field in the vicinity of the earth does not change significantly because the distance change from the earth to the moon is around 0.25% of the distance to the sun and hence the force difference is the inverse square of that.
Ahh ok, but how to explain in terms of gravitational potential?
0
6 years ago
#6
The gravitational potential difference, due to the Sun, between the Earth and Moon is negligible for the same reason.
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#7
Thanks to both of you!
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