For Q27a why do they discuss other features that are not related to temperature and chemical composition. Talking about density and translational and rotational velocities seems to not answer the question.
Gluons mediate the strong force. Photons mediate the electromagnetic force. EM waves interact through the electromagnetic force because they are themselves oscillating electric and magnetic fields perpendiclar to each other.
The initial value of r would be 6800km and the final value of r would be 42000km, you jusy multiply the denominator of the expression for U by 2 as the total energy of the satellite is given by E=1/2(U). Make sure to convert the values of r to meters
I don't think the formula is given in the formula sheet but it's the E=-GMm/2r formula for total energy. Just find the initial value of E using the initial orbital radius given and subtract it from the final value of E using the new orbital radius given.
Total energy way I think cause GPE way just tells you how much GPE it gained and doesn't account for the net decrease in kinetic energy of the satellite too.