Pendulum. A small rock with mass $0\mathrm{.}12$ kg is fastened to a massless string with length $0\mathrm{.}80$ m to form a pendulum. The pendulum is swinging so as to make a maximum angle of with the vertical. Air resistance is negligible. $($a$)$ What is the speed of the rock when the string passes through the vertical position? What is the tension in the string $($b$)$when it makes an angle of with the vertical, $($c$)$ as it passes through the vertical?