# Gravitational Potential A Level Question

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Planet N has a gravitational potential –V at its surface. Planet M has double the density and double the radius of planet N. Both planets are spherical and have uniform density.

What is the gravitational potential at the surface of planet M?

I am actually clueless, can anyone help me please?

What is the gravitational potential at the surface of planet M?

I am actually clueless, can anyone help me please?

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#3

radius= 2r so V=-GM/r so V/2

2* density so over the volume its 2V. Since it has 2R, volume increases by 2 and leads to potential = 4V

4/2= 2V

2* density so over the volume its 2V. Since it has 2R, volume increases by 2 and leads to potential = 4V

4/2= 2V

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(Original post by

2V

**UnknowNAlegend**)2V

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(Original post by

never mind i got it

**UnknowNAlegend**)never mind i got it

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#9

V=-GM/r

Planet N: density=d, radius= r, , mass=m, V=4/3 * pi * r^3 = volume of N

PlanetM: radius= 2r,

mass= density * volume

density=2d, volume= 4/3 *pi* (2r)^3= 4/3*pi* 8r^3= 8* volume of N

Mass= 2*8= 16m

Potential, V=-GM/r=16/2= 8V

Planet N: density=d, radius= r, , mass=m, V=4/3 * pi * r^3 = volume of N

PlanetM: radius= 2r,

mass= density * volume

density=2d, volume= 4/3 *pi* (2r)^3= 4/3*pi* 8r^3= 8* volume of N

Mass= 2*8= 16m

Potential, V=-GM/r=16/2= 8V

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#10

(Original post by

the answer is 8V, but I don't know the working out

**I-ZAAA**)the answer is 8V, but I don't know the working out

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(Original post by

V=-GM/r

Planet N: density=d, radius= r, , mass=m, V=4/3 * pi * r^3 = volume of N

PlanetM: radius= 2r,

mass= density * volume

density=2d, volume= 4/3 *pi* (2r)^3= 4/3*pi* 8r^3= 8* volume of N

Mass= 2*8= 16m

Potential, V=-GM/r=16/2= 8V

**UnknowNAlegend**)V=-GM/r

Planet N: density=d, radius= r, , mass=m, V=4/3 * pi * r^3 = volume of N

PlanetM: radius= 2r,

mass= density * volume

density=2d, volume= 4/3 *pi* (2r)^3= 4/3*pi* 8r^3= 8* volume of N

Mass= 2*8= 16m

Potential, V=-GM/r=16/2= 8V

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(Original post by

Not if it was -V on the first one.

**RogerOxon**)Not if it was -V on the first one.

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#13

Basically, Potential= -GM/r

For planet N, it has a radius, a density, a mass and a volume which I have labelled as letters for short.

For Planet M, the radius is twice of N's radius.

To find out M's mass, do volume* density

You're told M has two times density of N.

To find out volume of M, do 4/3*pi*r^3, however, this time, your radius is 2r since M is twice of radius of N. This results in 8 times the volume

Mass of N = 8*2=16 due to mass=density *volume

Sub in the mass and radius into V= -GM/r

soz about the calculations, only read your comment later lol

For planet N, it has a radius, a density, a mass and a volume which I have labelled as letters for short.

For Planet M, the radius is twice of N's radius.

To find out M's mass, do volume* density

You're told M has two times density of N.

To find out volume of M, do 4/3*pi*r^3, however, this time, your radius is 2r since M is twice of radius of N. This results in 8 times the volume

Mass of N = 8*2=16 due to mass=density *volume

Sub in the mass and radius into V= -GM/r

soz about the calculations, only read your comment later lol

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(Original post by

Basically, Potential= -GM/r

For planet N, it has a radius, a density, a mass and a volume which I have labelled as letters for short.

For Planet M, the radius is twice of N's radius.

To find out M's mass, do volume* density

You're told M has two times density of N.

To find out volume of M, do 4/3*pi*r^3, however, this time, your radius is 2r since M is twice of radius of N. This results in 8 times the volume

Mass of N = 8*2=16 due to mass=density *volume

Sub in the mass and radius into V= -GM/r

soz about the calculations, only read your comment later lol

**UnknowNAlegend**)Basically, Potential= -GM/r

For planet N, it has a radius, a density, a mass and a volume which I have labelled as letters for short.

For Planet M, the radius is twice of N's radius.

To find out M's mass, do volume* density

You're told M has two times density of N.

To find out volume of M, do 4/3*pi*r^3, however, this time, your radius is 2r since M is twice of radius of N. This results in 8 times the volume

Mass of N = 8*2=16 due to mass=density *volume

Sub in the mass and radius into V= -GM/r

soz about the calculations, only read your comment later lol

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(Original post by

Ok sure

**UnknowNAlegend**)Ok sure

A spacecraft of mass 1.0 × 106 kg is in orbit around the Sun at a radius of 1.1 × 1011 m

The spacecraft moves into a new orbit of radius 2.5 × 1011 m around the Sun.

What is the total change in gravitational potential energy of the spacecraft?

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(Original post by

Firstly list out your relevant equations for this one

**UnknowNAlegend**)Firstly list out your relevant equations for this one

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