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| <title>The radioactive core decayed into three fragments of mass m_1, m_2, and m_3, having mutually perpendicular velocities v_1, v_2, and v_3, respectively. What was the speed of the nucleus before the decay?</title> | | <title>The radioactive core decayed into three fragments of mass m_1, m_2, and m_3, having mutually perpendicular velocities v_1, v_2, and v_3, respectively. What was the speed of the nucleus before the decay?</title> |
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| <h3> Statement </h3> | | <h3> Statement </h3> |
| | | |
| <p> | | <p> |
| $2.2.16$ | | $2.2.16$ |
| The radioactive core decayed into three fragments of mass $m_1$, $m_2$, and $m_3$, having mutually perpendicular velocities $v_1$, $v_2$, and $v_3$, respectively. What was the speed of the nucleus before the decay? | | The radioactive core decayed into three fragments of mass $m_1$, $m_2$, and $m_3$, having mutually perpendicular velocities $v_1$, $v_2$, and $v_3$, respectively. What was the speed of the nucleus before the decay? |
| </p> | | </p> |
| <h3>Solution</h3> | | <h3>Solution</h3> |
| <p> | | <p> |
| Let's consider the following figure | | Let's consider the following figure |
| </p> | | </p> |
| <center> | | <center> |
| <figure> | | <figure> |
| <img src="draw.png" | | <img src="draw.png" |
| loading="lazy" alt="2.2.16" width="200" /> | | loading="lazy" alt="2.2.16" width="200" /> |
| <figcaption> | | <figcaption> |
| Velocity's analysis | | Velocity's analysis |
| </figcaption> | | </figcaption> |
| </figure> | | </figure> |
| </center> | | </center> |
| <p> | | <p> |
| From Momentum Conservation Law (MCL) | | From Momentum Conservation Law (MCL) |
| $$(m_1+m_2+m_3)~\vec{V} = m_1\vec{v_1}+m_2\vec{v_2}+m_3\vec{v_3}$$ | | $$(m_1+m_2+m_3)~\vec{V} = m_1\vec{v_1}+m_2\vec{v_2}+m_3\vec{v_3}$$ |
| Since velocity's vectors are mutually perpendicular, their directions can be fundamental for establishing the spatial coordinated system. So, let be $\hat{v_1}$, $\hat{v_2}$ and $\hat{v_3}$ the unitary vectors for each direction. Applying MCL for each direction, | | Since velocity's vectors are mutually perpendicular, their directions can be fundamental for establishing the spatial coordinated system. So, let be $\hat{v_1}$, $\hat{v_2}$ and $\hat{v_3}$ the unitary vectors for each direction. Applying MCL for each direction, |
| $$(m_1+m_2+m_3)V_1 = m_1v_1 \;(1)$$ | | $$(m_1+m_2+m_3)V_1 = m_1v_1 \;(1)$$ |
| $$(m_1+m_2+m_3)V_2 = m_2v_2 \;(2)$$ | | $$(m_1+m_2+m_3)V_2 = m_2v_2 \;(2)$$ |
| $$(m_1+m_2+m_3)V_3 = m_3v_3 \;(3)$$ | | $$(m_1+m_2+m_3)V_3 = m_3v_3 \;(3)$$ |
| where $V_1$, $V_2$ and $V_3$ are the components of velocity $\vec{V}$, | | where $V_1$, $V_2$ and $V_3$ are the components of velocity $\vec{V}$, |
| $$V=\sqrt{V_1^2+V_2^2+V_3^2} \;(4)$$ | | $$V=\sqrt{V_1^2+V_2^2+V_3^2} \;(4)$$ |
| Substituting $(1)$, $(2)$ and $(3)$ into $(4)$ | | Substituting $(1)$, $(2)$ and $(3)$ into $(4)$ |
| $$\boxed{V=\frac{\sqrt{m_1^2v_1^2+m_2^2v_2^2+m_3^2v_3^2}}{m_1+m_2+m_3}}$$ | | $$\boxed{V=\frac{\sqrt{m_1^2v_1^2+m_2^2v_2^2+m_3^2v_3^2}}{m_1+m_2+m_3}}$$ |
| </p> | | </p> |
| <p style="text-align: right; font-style: italic; font-size: 14;"> | | <p style="text-align: right; font-style: italic; font-size: 14;"> |
| BSc. Luis Daniel Fernández Quintana<br> | | BSc. Luis Daniel Fernández Quintana<br> |
| Physics Department (FCNE)<br> | | Physics Department (FCNE)<br> |
| Universidad de Oriente, Cuba<br> | | Universidad de Oriente, Cuba<br> |
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