Question

is work zero if the starting point and ending point of motion is the same

Answer 1

This is because the force is not in the same direction (the force is up) as the distance moved by the rock (eastward). If you do a full push-up, lifting yourself up and then back down, the total work is zero. This is because the total distance from the starting point to the ending point is zero.

Answer 2

When the starting point and the ending points are the same, the total work is zero. When the only forces that do work are conservative forces, the total mechanical energy E=K+U. Nonconservative ForcesThe friction force that acts on a crate sliding on a ramp, the body slides up and then back down to the starting point, the total work done on it by the friction force is not zero (W     other≠0).