Question

A $238U$ nucleus decays by emitting an alpha particle of speed $vms^{- 1}$. The recoil speed of the residual nucleus is (in $ms^{- 1}$)

• A. $- 4v/234$
• B. $v/4$
• C. $- 4v/238$
• D. $4v/238$

Answer 1

Answer: (A)

$- 4v/234$

Answer 2

Initially ²³⁸U nucleus was at rest and after decay its part moves in opposite direction.

According to conservation of momentum

$4 v + 234 V$ = 238 × 0 ⇒ $V = - \frac { 4 v } { 234 }$