An object, with mass 16 kg and speed 19 m/s relative to an observer, explodes into two pieces, one 4 times as massive as the other; the explosion takes place in deep space. The less massive piece stops relative to the observer. How much kinetic energy is added to the system during the explosion, as measured in the observer's reference frame? I calculated the original momentum, then i calculated the final momentum. I then solved for vfinal. I got 23.75 m/s for my vfinal. But now I tried calculating delta KE and I'm getting 1624.5 J, but my hw site is telling me it is incorrect. Can someone help me out?