Four forces of the same magnitude act on a square as shown in figure. The square can rotate about point $O$; mid point of one of the edges. The force which can produce greatest torque is

Uniform rod $AB$ is hinged at end $A$ in horizontal position as shown in the figure. The other end is connected to a block through a massless string as shown. The pulley is smooth and massless. Masses of block and rod is same and is equal to $m$. Then acceleration of block just after release from this position is

A cubical block of side $L$ rests on a rough horizontal surface with coefficient of friction $\mu .$ A horizontal force $F$ is applied on the block as shown If the coefficient of friction is sufficiently high so that the block does not slide before toppling, the minimum force required to topple the block is

In an experiment with a light beam balance, an unknown mass $m$ is balanced by two known masses of $16 \mathrm{kg}$ and $4 \mathrm{kg}$ as shown in figure. The value of the unknown mass $m$ is

A cube of side $a$ and mass $m$ is to be tilted at point $A$ by applying a force $F$ as shown in figure. The minimum force required is