A 113 kg man sits on the stern of a 6.3 m long boat. The prow of the
boat touches the pier, but the boat isn’t tied. The man notices his
mistake, stands up and walks to the boat’s prow, but by the time he
reaches the prow, it’s moved 3.26 m away from the pier. Assuming no
water resistance to the boat’s motion, calculate the boat’s mass (not
counting the man).

Is a  vector quantity  that refers to "the rate at which an object changes its position." imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. while this might result in a frenzy of activity, it would result in a zero velocity. because the person always returns to the original position, the motion would never result in a change in position. since velocity is defined as the rate at which the position changes, this motion results in zero velocity. if a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. every step must go into moving that person further from where he or she started. for certain, the person should never change directions and begin to return to the starting position.