1. The problem statement, all variables and given/known data A 34.0 g bullet travelling at 122 m/s emdeds itself in a wooden block on a smooth surface. The block then slides toward a spring and collides with it. The block compresses the spring, k=99.0 N/m, a maximum of 1.20 cm. Calculate the mass of the block of wood. 2. Relevant equations Eelasticpot= 1/2 k x^2 Ekinetic = 1/2 m v^2 m1v1=(m1+m2)(v2) 3. The attempt at a solution I've looked into this indepth online and found similar questions, but nothing where mass is the unknown. I have used law of conservation of energy ie. 1/2(0.034)(122)^2 = 1/2(0.034 + m)v^2 = 1/2(99)(0.012) to find the velocity of the block with the bullet lodged in it, (and likewise using my knowns to find the mass of the block), however this results in a rediculous 1207 kg, which seemed far too high. So, I need to know a better way to do this. One thing to point out (perhaps a flaw in my attempts), is that the kinetic energy of the bullet (before becoming enlodged) does not equal the elastic potential energy of the spring. Could this mean it is not a closed system. Thanks for any help, I know I'm new here but my friend and I have been working on this problem all weekend with no luck.