Please help! Is the description of how gravity works a scientific theory or a scientific law how do you know?

Rank the torques on the five doors shown in the figure above from least to greatest. note that the magnitude of all the forces is the same

Aproton is projected toward a fixed nucleus of charge +ze with velocity vo. initially the two particles are very far apart. when the proton is a distance r from the nucleus its velocity has decreased to 1/2vo. how far from the nucleus will the proton be when its velocity has dropped to 1/4vo?

Steam enters an adiabatic diffuser at 150 kpa and 1208c with a velocity of 550 m/s. determine the minimum velocity that the steam can have at the outlet when the outlet pressure is 300 kpa.