The mass of 2 particles A and B are 4kg & 5 kg respectively. Their velocities are 5m/s & 10m/s respectively in +x direction. Find the heat generated if both the particles are brought to rest by friction.In this question I can think of 2 ways-1. KE of A = 50 J & KE of B = 250 J => Total energy = 300 J. Hence heat released = 300 J2. velocity and mass of Centre of mass are 70/9 m/s and 9 kg respectively. So KEcom = 2450/9 & velocity of A & B relative to COM are -25/9 m/s and 20/9 m/s respectively. So KE of A and B relative to COM =3125/162 J & 1000/81 respectively. Hence total energy = 49225/162 J. Hence energy released = 49225/162 J.Both the methods seem right in their own way. Can anyone tell me which is actually right and why?