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This will really help you learn a lot.
The change in gravitational potential energy due to change in position must be the change in it's kinetic energy as the system is isolated! so find out the potential energies of the two different points!
<span>PE=−[G<span>M1</span><span>M2</span>]÷R
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Potential energy of a particle due to mass A is not affected by presence of any other mass B !</span>
To answer these questions just use the equations for potential energy using the mass and heights described. the potential energy at the prescribed heights = the initial kinetic energy required to reach that height.
Make sure you calculate the force of gravity on the surface using the radius of the planet.
It is correct, the action is paddling, where you move the water backwards, and the reaction is the boat moving forwards.