In a race as runners cross the finish line. why do they continue to move a few steps before halting

Karen is waiting by the lockers before school for her friend richard. they had agreed to look over the history review sheet together to be ready for the test later that day. richard shows up late with uncombed hair and wrinkled clothes. karen: "you're five minutes late and you look like a wreck! " richard: (slams his locker) "you know, i don't have time for this." karen: "fine! figure out the test on your own! "