Physics - NLM Question with Solution | TestHub

F.B.D's of both the blocks before cutting the thread :

$\mathrm{kx}=\mathrm{mg}$ (blocks are in equilibrium before cutting the thread)

Now thread is cut, spring force will not be able to change its value instantaneously, hence its value remains unchanged. But since, thread is cut tension T will vanish. Now FBD's after thread is cut :

$\mathrm{mg}-\mathrm{kx}=\mathrm{ma}[\mathrm{kx}=\mathrm{mg}]$ $\mathrm{mg}-\mathrm{mg}=\mathrm{ma}$ $\mathrm{a}=0$ - acceleration of block B is 0.