Overhead SwingHardQuestion 30655
Question
A ball is swung in a vertical circle overhead (as in a sling). At the lowest point, the string is taut. If the ball barely completes the circle (v_top = √gr), the speed at the lowest point is:
- A√(3gr)
- B√(5gr)Correct
- C√(7gr)
- D√(gr)
Correct answer
√(5gr)
Explanation
Energy conservation from bottom to top: ½mv_b² = ½mv_t² + mg(2r). v_t = √(gr). v_b² = gr + 4gr = 5gr → v_b = √(5gr).