Assignment:
A ball of mass m is attached to a string of length L. It is being swung in a vertical circle with enough speed so that the string remains taut throughout the ball's motion. Assume that the ball travels freely in this vertical circle with negligible loss of total mechanical energy. At the top and bottom of the vertical circle, the ball's speeds are v_t and v_b, and the corresponding tensions in the string are T_t and T_b. T_t and T_b (vectors) have magnitudes T_t and T_b.
Find T_b - T_t, the difference between the magnitude of the tension in the string at the bottom relative to that at the top of the circle.
Express the difference in tension in terms of m and g. The quantities v_t and v_b should not appear in your final answer.