c
(c)\(\frac{{\Delta K}}{K} = \left[ {1 - {{\left( {\frac{{{m_1} - {m_2}}}{{{m_1} + {m_2}}}} \right)}^2}} \right] = \left[ {1 - {{\left( {\frac{{m - 2m}}{{m + 2m}}} \right)}^2}} \right]\)\( = \frac{8}{9}\)
\(\Delta K\)=\(\frac{8}{9}K\)i.e. loss of kinetic energy of the colliding body is \(\frac{8}{9}\) of its initial kinetic energy.