Ta có: \({W_d} = W - {W_{\rm{t}}} = \frac{1}{2}m{\omega ^2}\left( {{A^2} - {x^2}} \right) = \frac{1}{2} \cdot 0,2 \cdot {5^2} \cdot \left( {0,{{06}^2} - 0,{{02}^2}} \right) = 8 \cdot {10^{ - 3}}{\rm{\;J}} = 8{\rm{\;mJ}}.\)