- The gravitational pull exerted by the earth on the spacecraft is inversely proportional to the square of its distance from the centre of the earth. So if this force is N, the mass of the spacecraft is kg, and its distance is m from the centre of the earth,
- At the earth's surface this pull is equal to the weight of the spacecraft; i.e. when N. This enables you to find .
- When the spacecraft moves outwards from the earth from to , the work done on it by the earth's gravitational pull is:
- Then use the Work-Energy Principle to find the initial velocity knowing that the final velocity is zero.
If it still doesn't work out, show us your working so far, and we'll have another look at it.