For elastic collisions, the fraction of kinetic energy transferred to the second mass is given by:
\[
K = \frac{4 m_1 m_2}{(m_1 + m_2)^2}
\]
To maximize \( K \), differentiate with respect to \( \frac{m_2}{m_1} \), and solving gives:
\[
m_1 = m_2
\]
Thus, the kinetic energy transfer is maximum when \( m_1 = m_2 \), i.e.,