Problem 5.56

จาก \(\Sigma W = \Delta K\)

\(W_{n}+ W_{g}+ W_{s}+ W_{f}= \Delta K\)

จาก \(u = 0 m/s \to K_{i}= 0\)

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

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

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

\(-mg(xsin\theta -0)-\frac{1}{2}k(0^{2}-\ell ^{2})-\mu mgxcos\theta =0\)

\(\therefore x =\frac{k\ell ^{2}}{2mgsin\theta (1 + \mu \cot \theta )}\;\blacksquare\)