Question

Find the energy necessary to put 5kg , initially at rest on Earth's surface, into geosynchronous orbit.

do i use the formula U=-GMm/r

I get 290 MJ?

Answer 1

You also need to consider the kinetic energy, unless you are thinking of using a giant space elevator (in that case you get the kinetic energy free of charge from the Earth's rotational energy).

Answer 2

What do you mean by the kinetic energy it hasn't given me anything

Answer 3

First you need to look up or compute the radial distance of the satellite from the center of the earth. It is about 41,000 km.

Then you need to provide not only the larger potential energy to get the satellite that high up, but also provide enough kinetic energy in the circular orbit to let the satellite maintain that orbital altitude.