Serway & Jewett — Conservation of Energy: Problem 38

Why is the following situation impossible? An athlete tests her hand strength by having an assistant hang weights from her belt as she hangs onto a horizontal bar with her hands. When the weights hanging on her belt have increased to 80% of her body weight, her hands can no longer support her and she drops to the floor. Frustrated at not meeting her hand-strength goal, she decides to swing on a trapeze. The trapeze consists of a bar suspended by two parallel ropes, each of length \(\ell\), allowing performers to swing in a vertical circular arc (Fig. P8.38). The athlete holds the bar and steps off an elevated platform, starting from rest with the ropes at an angle \(\theta_i = 60.0^\circ\) with respect to the vertical. As she swings several times back and forth in a circular arc, she forgets her frustration related to the hand-strength test. Assume the size of the performer’s body is small compared to the length \(\ell\) and air resistance is negligible.