Áp dụng ptr cân bằng nhiệt, ta có:
\(\left[{}\begin{matrix}I:m_0c_0\left(t_1-t_0\right)=mc\left(t-t_1\right)_{\left(1\right)}\\II:\left(m_0c_0+mc\right)\left(t_2-t_1\right)=mc\left(t-t_2\right)_{\left(2\right)}\end{matrix}\right.\)
Lấy (2) - (1), ta có: \(\left(m_0c_0+mc\right)\left(t_2-t_1\right)-m_0c_0\left(t_1-t_0\right)=mc\left(t-t_2\right)-mc\left(t-t_1\right)\)
\(\Leftrightarrow4\left(m_0c_0+mc\right)-6\left(m_0c_0\right)=mc\left(t_1-t_2\right)-4mc\)
\(\Leftrightarrow8mc=2m_0c_0\)
\(\Leftrightarrow\dfrac{m_0c_0}{mc}=4\)
Áp dụng PTCBN, ta có: \(III:\left(m_0c_0+2mc\right)\left(t_3-t_2\right)=mc\left(t-t_3\right)_{\left(3\right)}\)
Lấy (3) - (2), ta có: \(\left(m_0c_0+2mc\right)\left(t_3-t_2\right)-\left(m_0c_0+mc\right)\left(t_2-t_1\right)=mc\left(t-t_3\right)-mc\left(t-t_2\right)\)
\(\Leftrightarrow6mc\left(t_3-t_2\right)-20mc=mc\left(t_2-t_3\right)-mc\left(t_3-t_2\right)\)
\(\Leftrightarrow7mc\left(t_3-t_2\right)=20mc\)
\(\Rightarrow\Delta t_{32}=\left(t_3-t_2\right)=\dfrac{20}{7}\approx2,85^0C\)
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