Đáp án:
\({l_2} = 28cm\)
Giải thích các bước giải:
Tóm tắt:
\(\begin{array}{l}{l_0} = 20cm\\{l_1} = 24cm;{F_{dh1}} = 5N\\{F_{dh2}} = 10N;{l_2} = ?\end{array}\)
Giải:
Ta có: \({F_{dh}} = k.\Delta l \Rightarrow \left\{ \begin{array}{l}{F_{dh1}} = k.\Delta {l_1} = k.\left( {{l_1} - {l_0}} \right)\\{F_{dh2}} = k.\Delta {l_2} = k.\left( {{l_2} - {l_0}} \right)\end{array} \right.\)
\(\begin{array}{l} \Rightarrow \frac{{{F_{dh1}}}}{{{F_{dh2}}}} = \frac{{{l_1} - {l_0}}}{{{l_2} - {l_0}}} \Leftrightarrow \frac{{24 - 20}}{{{l_2} - 20}} = \frac{5}{{10}}\\ \Leftrightarrow \frac{4}{{{l_2} - 20}} = \frac{1}{2} \Rightarrow {l_2} = 28cm\end{array}\)
