Đáp án:
676J
Giải thích các bước giải:
\[\begin{array}{l}
{{\rm{W}}_{d1}} = \frac{1}{2}mv_1^2 = 81\\
{{\rm{W}}_{d2}} = \frac{1}{2}mv_2^2 = 64\\
\frac{{{{\rm{W}}_{d1}}}}{{{{\rm{W}}_{d2}}}} = {\left( {\frac{{{v_1}}}{{{v_2}}}} \right)^2} = \frac{{81}}{{64}} \Rightarrow \frac{{{v_1}}}{{{v_2}}} = 1,125 \Rightarrow {v_1} = 1,125{v_2}\\
{v_3} = 2{v_1} + {v_2} = 2.1,125{v_2} + {v_2} = 3,25{v_2}\\
\frac{{{{\rm{W}}_{d3}}}}{{{{\rm{W}}_{d2}}}} = {\left( {\frac{{{v_3}}}{{{v_2}}}} \right)^2} = 3,{25^2} = \frac{{{{\rm{W}}_{d3}}}}{{64}} \Rightarrow {{\rm{W}}_{d3}} = 676J
\end{array}\]
