went through all the similar questions in the forum and failed to find a similar one to mine. Question: On a frictionless table there are two masses , one of size m with velocity V0 (I'll call it the small mass) and one with mass M that is currently resting (the "big" mass). We connect a spring (with spring constant k,and l0 is its resting length) to the big mass so that the small one hits it and sticks to it, while not losing any energy. What is the velocity of the big Mass as a function of its location regarding the center of mass? (After the collision) My attempt: First of all, I know that the velocity of the CM is constant. I tried writing the energy equation and start from it: E=0.5mV1^2+0.5MV2^2+0.5k(X2-X1-l0)^2 = 0.5mV0^2 V1-Speed of mass m, V2-Speed of mass M, X1,X2 - locations as above. After rearranging the equation I only needed to find V1 but I failed to do so. I tried from the momentum equation but it didn't help. Note: I am not suppose to solve any ODE or use the fact that we have harmonic movement. *Also, Is there a guide on how to write math equations here?