[Tex/LaTex] Left alignment of multiple equations with one label

Question

I am using flalign for left alingment of two equations, but I also want to give them one label for which I found the split environment. But they are not working together.
The question is how to align left two equations but give them one common label?

Answer 1

The question is not yet clear, do you mean one of the following variations of the theme?

\documentclass{article}
\usepackage{amsmath}

\begin{document}
  \hrule
  \begin{flalign}
    \begin{gathered}
      \text{First equation.}\hfill\\
      \text{Second equation.}
    \end{gathered}
    &&
  \end{flalign}
  \hrule
  \begin{flalign}
    \begin{gathered}
      \text{Bla} \\
      \text{Centered}
    \end{gathered}
    &&
  \end{flalign}
  \hrule
  \begin{flalign}
    \begin{aligned}
      1 + 2 &= 3 \\
      4 &= 2^2 * 2^0
    \end{aligned}
    &&
  \end{flalign}
  \hrule
\end{document}

Variations with updated information. The first case puts all to the left, the second case is more complicate, it sets the equations in the middle, but the text to the left:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\hrule
\begin{flalign}
  \begin{aligned}
    \text{or}\quad f &= m \frac{dv}{dt};\\
    \text{or}\quad f &= m \frac{d^2y}{dt^2};
  \end{aligned}
  &&
\end{flalign}
\hrule
\begin{flalign}
  \begin{gathered}
    \rlap{or}\vphantom{\frac{dv}{dt}} \\
    \rlap{or}\vphantom{\frac{d^2y}{dt^2}}
  \end{gathered}
  &&
  \begin{aligned}
    f &= m \frac{dv}{dt};\\
    f &= m \frac{d^2y}{dt^2};
  \end{aligned}
  &&
\end{flalign}
\hrule
\end{document}