Two balls of equal masses moving with $\;10 \;ms^{-1}\;$ towards each other collide after some time . Considering the collision to be inelastic & mass of each ball to be 1 kg , the thermal energy developed in the process is equal to what?

Question

$(a)\;10\;J\qquad(b)\;5\;J\qquad(c)\;100\;J\qquad(d)\;50\;J$