\(0= m _{1} v _{1}+ m _{2} v _{2}\)

\(\therefore 0=12 \times 4+4 \times v _{2}\)

\(\therefore 4 v _{2}=-48\)

\(\therefore v _{2}=-12 m / sec\)

બીજી ટુકડાની ગતિઊર્જા \(=\frac{1}{2} m _{2} v _{2}^{2}\)

\(=\frac{1}{2} \times 4 \times(-12)^{2}\)

\(=\frac{1}{2} \times 4 \times 144\)

\(=288\; J\)