$A$ uniform meter scale is balanced at the $30 \ cm$ mark on a knife edge,when weights of $60 \ N$ and $10 \ N$ are suspended at the $10 \ cm$ and $80 \ cm$ marks,respectively. The mass of the meter scale is: $(g = 10 \ m/s^2)$ (in $kg$)

$A$ $3\; m$ long ladder weighing $20\; kg$ leans on a frictionless wall. Its feet rest on the floor $1\; m$ from the wall as shown in the figure. Find the reaction forces of the wall and the floor.

Two men are carrying a uniform bar of length $L$ on their shoulders. The bar is held horizontally such that the younger man gets $(1/4)^{th}$ of the total load. Suppose the younger man is at one end of the bar,what is the distance of the other man from the other end?

Write the conditions for the equilibrium of a rigid body.

Explain the construction and working of an ideal lever and also explain the principle of moments of force.

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