I have an object number 1 (M1) and second object number 2 (M2). Mass of number 1 is known and number 2 is unknown. And M1 << M2. Both massess are attached to a spring with spring constant k, where k is known. Also the period T is known. How do I solve mass number 2? The system: ---<spring>--- M1-|||||||-M2 No gravitation, mass of the spring is negligible and so is friction in the system.