people who do chin-ups raise their chin just over a bar, supporting themselves only by their arms. typically, the body below the arms is raised by
about 30 cm in a time of 1 s, starting from rest. assume that the entire body of a 680 n person who is chinning is raised this distance and that 0.5 s
is spent accelerating upward and 0.5s accelerating downward, uniformly in both cases. find the force his arms must exert on him during the
accelerating part of the chin-up.
762 n
742 n
705 n
700 n