Problem 5.57

จาก \(\Sigma W = \Delta K\)

L

\(\theta\)

\(W_{n}+ W_{T}+ W_{g}+ W_{s}= \Delta KLcos\theta\)

L

จาก \(u = 0 m/s \to K_{i}= 0m\)

และ \(v = 0 m/s \to K_{f}= 0\therefore \Delta K = 0\)

จะได้ \(W_{n}+ W_{T}+ W_{g}+ W_{s}= 0\)

\(0 + 0 - mg(y_{f}- y_{i})-\frac{1}{2}k(x_{f}^{2} - x_{i}^{2}) = 0\)

\(-mg(0-L(1-\cos \theta ))-\frac{1}{2}k(x^{2}-0^{2})=0\)

\(\therefore x =\sqrt{\frac{2mgL(1-\cos \theta )}{k}}\;\blacksquare\)