A mass M attached to a spring oscillates with a period of 2 s. If the mass is increased by 2kg, the period increases by one second. The initial mass M (in kg) is ______.

We know that for a spring block system T=2πMkHere k = spring constant. In first case, 2=2πMk  ……….(i) In second case, 3=2πM+2k ………(ii)Squaring of Eqs. (i) and (ii) and then dividing (ii) by (i), we have94=M+2M=1+2MSolving we get M = 1.6 kg.