https://www.vtomb.com/video/_FbqYwmiYwI&list=PLF_7kfnwLFCGAL8XxoX2I8SjMXMtc07Yt&index=7/centre-of-mass-07-collision-series-01-elastic-collisions-in-1-d-iit-jee-mains-neet-video