Okay, the problem is: A [itex]1200~kg[/itex] satellite is in a circular orbit around the Earth at a radius of [itex]8.77\cdot 10^6~m[/itex]. What is the work done by gravity when the satellite has gone a quarter of the war around its orbit? The acceleration due to gravity at the height of the satellite is [itex]5.19\cdot ~m/s^2[/itex] Well, I figured, that since calculation involves the satellite not making a full rotation (a zero displacement, the work done done would be a nonzero value. Apparently, though, this isn't true, and it is indeed zero. Why is this true?