Question

Initially the system shown in figure is in equilibrium. At the moment the string is cut, the downward acceleration of blocks A and B are respectively $a_1$ and $a_2$. The magnitudes of $a_1$ and $a_2$ are (Given acceleration due to gravity $=g$):

• A. Zero and zero
• B. $2g$ and zero
• C. $g$ and zero
• D. Zero and $3g$

Answer 1

The correct option is B $2g$ and zero

$T=2mg$
As soon as string is cut T (on A) suddenly becomes zero. Therefore a force of $2mg$ acting on upward direction on A suddenly becomes zero.
So net force on it will become $2mg$ downwards.
$\therefore a_1=\frac{2mg}{m}=2g$ (downwards)
Spring force does not become instantly zero. So acceleration of B will not change abruptly.
or $a_2=0$