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Q.
A nucleus of $_{84} Po ^{210}$ originally at rest emits an $\alpha$ -particle with speed $v$. What will be recoil speed of the daughter nucleus?
Nuclei
Solution:
Applying principle of conservation of linear momentum,
$m_{\alpha} v_{\alpha}+m_{N} v_{N}=0$
$4 v+(210-4) v_{N}=0$ or $v_{N}=\frac{-4 v}{206}$
Negative sign for recoil speed.