Two plates each of the mass m are connected by a massless spring as shown. A weight W is put on the upper plate which compresses the spring further. When W is removed, the entire assembly jumps up. The minimum weight W needed for the assembly to jump up when the weight is removed is just more than -

Step-by-step solution

For lower block +ve lift, kx mg x mg k W/E theorem array l - mg ( h + x )+ ( 1 2 kh ²- 1 2 kx ² )=0-0 - mgh - m ² ~g ² k + 1 2 kh ²- 1 2 m ² ~g ² k =0 kh ² 2 - mgh - 3 ~m ² ~g ² 2 k =0 ~h = mg m ² ~g ²+3 ~m ² ~g ² k = mg 2 mg k = 3 mg k , - mg k h = 3 mg k W + mg = kh W + mg =3 mg W =2 mg array