CP BIO Forces During Chin-ups.? When you do a chin-up, you raise your chin just over a bar (the chinning bar), sup-porting yourself with only your arms. Typically, the body below the arms is raised by about 30 cm in a time of 1.0 s, starting from rest. Assume that the entire body of a 680-N person doing chin-ups is raised by 30 cm, and that half the 1.0 s is spent accelerating upward and the other half accelerating downward, uniformly in both cases. Draw a free-body diagram of the person’s body, and use it to find the force his arms must exert on him during the accelerating part of the chin-up.
Solution 61P Step 1 The free body diagram is shown below: Here F represents the force applied by his arm and mg represents his weight.