11.
Ta có: \(\left\{ \begin{array}{l}
{P_1} = k\left( {{l_1} - {l_0}} \right)\\
{P_2} = k\left( {{l_2} - {l_0}} \right)
\end{array} \right.\)
Suy ra: \(\dfrac{{{P_1}}}{{{P_2}}} = \dfrac{{{l_1} - {l_0}}}{{{l_2} - {l_0}}} \Rightarrow \dfrac{5}{2} = \dfrac{{72,5 - {l_0}}}{{65 - {l_0}}} \Rightarrow {l_0} = 60cm = 0,6m\)
Độ cứng của lò xo là:
\(k = \dfrac{{{P_1}}}{{{l_1} - {l_0}}} = \dfrac{5}{{0,65 - 0,6}} = 100N/m\)
13.
Ta có:
\(\dfrac{{{P_1}}}{{{P_2}}} = \dfrac{{{l_1} - {l_0}}}{{{l_2} - {l_0}}} \Rightarrow \dfrac{{0,15}}{{0,1}} = \dfrac{{33 - 30}}{{{l_2} - 30}} \Rightarrow {l_2} = 32cm = 0,6m\)
