If we say that the escape velocity from a planet is say 10 km/s we think that a slower body will move away from that planet but will be eventually forced to fall back on the planet. In simple words we don't say the body won't move at all but it couldn't leave for ever the planet. What is confusin...

When we add who spin operators, one in $x$ and the other in $z$ direction, dose it make any physical sense? Do the eigenvalues of this sum is also equal to a sum of their eigenvalues?