You have answered that Newton’s Second Law of Motion is generally valid.

Your answer is right!

Defined as a time derivative of momentum the “Lex Secunda” is universally valid:

\[\vec{F} = \frac{d(m\vec{v})}{dt} = m\frac{d\vec{v}}{dt} + \vec{v}\frac{dm}{dt}\]

In this way, changes in mass at relativistic speeds are taken into account.

Please read on. See what Richard Feynman writes about it.

You can justify your answer with a comment.