A body of mass 4 kg moving with a velocity of 6 m/s collides with a stationary body of mass 2 kg and they move together after the collision. What is the kinetic energy lost during the collision?

By conservation of momentum: (4)(6) = (4+2)v, so v = 24/6 = 4 m/s. Initial KE = ½(4)(6²) = 72 J. Final KE = ½(6)(4²) = 48 J. KE lost = 72 - 48 = 24 J. Options B and C represent the final and initial kinetic energies respectively, common errors when candidates forget to subtract.