Physics - NLM Question with Solution | TestHub

In equilibrium the pulley is at rest, so net force on it is zero - (A) wrong.

Balancing forces on pulley + block gives spring force $Kx=3mg$, so elongation $x=\frac{3mg}{K}$ - (B) correct.

When block m is detached, the spring still pulls up with $3mg$ on pulley of mass m: $3mg-mg=ma\Rightarrow a=2g\uparrow$ - (C) correct, (D) wrong.

Answers: (B), (C).