An isolated spherical planet of radius R may be assumed to have all its mass concentrated at
its centre. The gravitational potential at the surface of the planet is − 6.30 × 107 J kg−1.
A stone of mass 1.30 kg is travelling towards the planet such that its distance from the centre
of the planet changes from 6R to 5R.
Calculate the change in gravitational potential energy of the stone.

Question

An isolated spherical planet of radius R may be assumed to have all its mass concentrated at
its centre. The gravitational potential at the surface of the planet is − 6.30 × 107 J kg−1.
A stone of mass 1.30 kg is travelling towards the planet such that its distance from the centre
of the planet changes from 6R to 5R.
Calculate the change in gravitational potential energy of the stone.

isaiah.feynman · Answer

|dw:1411502242775:dw|

anonymous · Answer

For distances greater than R, the potential energy varies inversely as r, combine that with the information given in the question.

anonymous · Answer

If you say the potential energy is k/r, then knowing the value at the surface of the planet lets you figure out k, then you can work out the potential energy at any other value of r>R