1. The problem statement, all variables and given/known data One end of a light elastic string having a natural length of 'a' and elastic modulus 'mg' is attached to 'm' mass and the other end to point 'O'. Then the mass is projected upwards.Where is the center of SHM? 2. Relevant equations ω=angular velocity F=ma from Hooke's law, T=λx/l T=tension of the string λ=elastic modulus l=natural length x=extention 3. The attempt at a solution There's no any equilibrium in the motion above point 'O' as T and mg are towards the same direction.But after point 'A' I think that there's a SHM as the string is extended.In the calculation, it says that center of SHM is at point 'O'..How can it be true ?...No equilibrium there !....It must be somewhere under that point 'O' where the two forces on the mass are opposing each other..Or where have I got it wrong ? thanks !