Đáp án:
\(\begin{array}{l}
3.\\
v = \frac{{20}}{7}m/s\\
4.\\
a.\\
v = 8,8m/s\\
b.\\
v = 0,8m/s
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
3.\\
p = p'\\
{m_1}{v_1} = ({m_1} + {m_2})v\\
v = \frac{{{m_1}{v_1}}}{{{m_1} + {m_2}}} = \frac{{0,5.4}}{{0,5 + 0,2}} = \frac{{20}}{7}m/s\\
4.\\
{p_1} = {m_1}{v_1} = 0,2.10 = 2kg.m/s\\
{p_2} = {m_2}{v_2} = 0,3.8 = 2,4m/s\\
a.\\
p = p'\\
{p_1} + {p_2} = ({m_1} + {m_2})v\\
v = \frac{{{p_1} + {p_2}}}{{{m_1} + {m_2}}} = \frac{{2 + 2,4}}{{0,2 + 0,3}} = 8,8m/s\\
b.\\
p = p'\\
|{p_1} - {p_2}| = ({m_1} + {m_2})v\\
v = \frac{{|{p_1} - {p_2}|}}{{{m_1} + {m_2}}} = \frac{{|2 - 2,4|}}{{0,2 + 0,3}} = 0,8m/s
\end{array}\)
