3.

\begin{figure}[h]
\begin{center}
  \includegraphics[alt={},max width=\textwidth]{a9f91ceb-662a-40cd-956b-815052b8f1a0-02_280_428_340_516}
\captionsetup{labelformat=empty}
\caption{Fig. 3}
\end{center}
\end{figure}

Two particles $A$ and $B$ have masses $3 m$ and $k m$ respectively, where $k > 3$. They are connected by a light inextensible string which passes over a smooth fixed pulley. The system is released from rest with the string taut and the hanging parts of the string vertical, as shown in Fig. 3. While the particles are moving freely, $A$ has an acceleration of magnitude $\frac { 2 } { 5 } g$.
\begin{enumerate}[label=(\alph*)]
\item Find, in terms of $m$ and $g$, the tension in the string.\\
(3 marks)
\item State why $B$ also has an acceleration of magnitude $\frac { 2 } { 5 } g$.
\item Find the value of $k$.
\item State how you have used the fact that the string is light.\\
(1 mark)
\end{enumerate}

\hfill \mbox{\textit{Edexcel M1  Q3 [9]}}