You catch a volleyball (mass 0.270 kg) that is moving downward at 7.50 m/s. In stopping the ball, your hands and the volleyball descend together a distance of 0.150 m. How much work do your hands do on the volleyball in the process of stopping it?

What is the magnitude of the force (assumed constant) that your hands exert on the volleyball?

P/s: I was able to figure out the first part. I just didn't understand why instead of using s = h + 0.15 (I choose the origin at where the hands haven't moved), h is the distance where the ball has the velocity of 7.5 m/s. The work done by hands on ball is the negative work that the ball exerts on hands after moving a distance of h above the origin and 0.15 below the origin?