Someone please help on A level physics question?

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Minnie16
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Could someone give me a clue on what equation to use please? I just can't get a right answer.

A rocket of mass 35 kg launched from the Earths surface gains 70 MJ of gravitational potential energy when it reaches maximum height.

a) Calculate the gravitational potential difference between the Earths surface and the highest point reached by the rocket.

Thanks!
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Sb22312
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The gravitational potential is just the mass specific gravitational potential energy, i.e. gravitational potential energy per unit mass. So gpe/m
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Minnie16
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(Original post by Sb22312)
The gravitational potential is just the mass specific gravitational potential energy, i.e. gravitational potential energy per unit mass. So gpe/m
So just 70 000 000/35 ?

But why?
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Sb22312
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(Original post by Jas1947)
So just 70 000 000/35 ?

But why?
So gravitational potential = -GM/r , and gravitational potential energy = -GMm/r, Gravitational potential energy is the energy required to move a point object from infinity (ie where the force of gravity is zero) to that point, so the formula takes into account the two masses (M and m) Gravitational potential can be thought of as the strength of the field, so the formula is more simple, as its just dependant on the mass of the object, how strong the field is, and how far away it is from the centre of the field
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Minnie16
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So could I think of it this way:
mgh=gravitational potential energy

And since V=gh I can rewrite this equation as mV=gravitational potential energy
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Sb22312
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(Original post by Jas1947)
So could I think of it this way:
mgh=gravitational potential energy

And since V=gh I can rewrite this equation as mV=gravitational potential energy
Not really as those equations only apply on the "surface" of the earth
If you are in space g is not constant, the equations in my previous answer are what you use
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Minnie16
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Ahh so since gravitational potential energy=GMm/r and since potential energy is V=GM/r we can sub these two equations to simply to get gravitational potential energy=Vm?
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Sb22312
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(Original post by Jas1947)
Ahh so since gravitational potential energy=GMm/r and since potential energy is V=GM/r we can sub these two equations to simply to get gravitational potential energy=Vm?
Yeah that's it
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Minnie16
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Thank you so much!
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