Hi, I like to ponder basic physics puzzles to pass time in boring meetings on metro etc...but I have one that I don't understand and I am obsessing over it (to detriment of working out etc.) it should be easy but I don't understand. Problem: Imagine you have two blocks (Mass of Block 1 is 1Kg...Mass of Block is 10Kg). They are free floating in space (no friction/air/gravity). They are 10meters apart from each other. If they both feel a force of 50 Newtons in opposite directions (towards each other). And then hit each other in an inelastic collision...what is the velocity of the final composite mass? My thought is ... 50 Newtons = 1kg * (acceleration)...so acceleration of block 1 is 50(m/S^2). I don't know how to determine the time the block is accelerating but I am thinking it is the same time as block 2 so I just make it accelerate for 1 second. So final velocity is 1 second * 50m/s^2 so...total energy at collision is .5*1kg * 2500= joules of energy for block 1. Then I do the second block and the total energy is 1 second * 10Kg* 5m/s^2 so total energy at collision is 125 Joules. Then I would take 2500 Joules and subtract 125 joules and then my net total energy is 2375 Joules going in the direction of block 1 so...the total velocity would be ((2375*2)/11Kg)^.5 = 20.7m/s going in the direction that block 1 was moving. But...the actual answer is 0 velocity with each block cancelling each other out...am I wrong? or is the answer wrong?