How to solve

A Uranium$-238$ nucleus $(U^{238})$ decays to a Thorium$-234(T{h}^{234})$ by emitting an alpha particle $($i$.$e$.$ a Helium$-4$ nucleus$)$: $U_{92}^{238}T{h}_{90}^{234}+H{e}_2^4$

A Uranium nucleus has $92$ protons in it while a Helium nucleus has $2$ protons. The mass of a Helium nucleus is $6\mathrm{.}645{10}^{-27}kg.$ For this problem assume that the Uranium nucleus is initially at rest and the Thorium nucleus remains at rest after the decay.

If the alpha particle is initially at rest at $190$ fm away from the Thorium nucleus:

$($A$)$ How fast is it moving when it is $380fm$ away from the Thorium nucleus?

$v_f=$

$($B$)$ How fast is it moving when it is very far away from the Thorium nucleus?

$v_f=$