Two particles of masses m1 and m2 move along the same straight line with velocities v1 and v2 respectively and stick together after they collide. Which one of the following expressions gives the kinetic energy of the composite particle immediately after the collision?
a) 21(m1v12+m2v22)
b) 2(m1+m2)m1m2(v1−v2)2
c) 2(m1+m2)(m1v1+m2v2)2
d) 2(m1+m2)(v1+v2)2