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Help please! - Multiple Choice - Gravitational Fields

Mars has a diameter approximately 0.5 that of the Earth, and a mass of 0.1 that of the Earth.

Mars has a diameter approximately 0.5 that of the Earth, and a mass of 0.1 that of the Earth.

If the gravitational potential at the Earth’s surface is –63 MJ kg–1, what is the approximate value of the gravitational potential at the surface of Mars?

A: –13 MJ kg–1

B: –25 MJ kg–1

C: –95 MJkg–1

D: –320 MJ kg–1

Reason for answer please?! Thanks!

(edited 9 years ago)
Original post by Jordan Jones
Mars has a diameter approximately 0.5 that of the Earth, and a mass of 0.1 that of the Earth.

Mars has a diameter approximately 0.5 that of the Earth, and a mass of 0.1 that of the Earth.

If the gravitational potential at the Earth’s surface is –63 MJ kg–1, what is the approximate value of the gravitational potential at the surface of Mars?

A: –13 MJ kg–1

B: –25 MJ kg–1

C: –95 MJkg–1

D: –320 MJ kg–1

Reason for answer please?! Thanks!



Do you have an idea of how to start? We can work from there.
Reply 2
Avatar for Jordan Jones
Jordan Jones
OP
Original post by randlemcmurphy
Do you have an idea of how to start? We can work from there.


The formulas given to us for Grav potential are:

(delta)W = m(delta)V

V = - GM/r

g = -(delta)V/(delta)r
So we know the formula for gravitational potential is V=-GM/r (symbols have their usual meaning)

Take all these values as 1 for Earth, -GM/r = -63 MJkg^-1

We also know that the mass of Mars is 0.1M and the radius is 0.5r

So put these values into the formula and you end up with V=0.2(-GM/r)

Since you are given the value of -GM/r, multiply it by 0.2 and you'll get the gravitational potential at the surface of Mars.

Hope this helps.
Original post by Jordan Jones
The formulas given to us for Grav potential are:

(delta)W = m(delta)V

V = - GM/r

g = -(delta)V/(delta)r


I think you have to use the idea that V is directly proportional to M/r, do you know what to do then?
Reply 5
Avatar for Jordan Jones
Jordan Jones
OP
Original post by CaitlinDy
So we know the formula for gravitational potential is V=-GM/r (symbols have their usual meaning)

Take all these values as 1 for Earth, -GM/r = -63 MJkg^-1

We also know that the mass of Mars is 0.1M and the radius is 0.5r

So put these values into the formula and you end up with V=0.2(-GM/r)

Since you are given the value of -GM/r, multiply it by 0.2 and you'll get the gravitational potential at the surface of Mars.

Hope this helps.


That helped a lot, thank you!

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