$A$ $2 \,m$ long rod of radius $1 \,cm$ which is fixed from one end is given a twist of $0.8$ radians. The shear strain developed will be

Wires $W_{1}$ and $W_{2}$ are made of the same material having a breaking stress of $1.25 \times 10^{9} \, N/m^{2}$. $W_{1}$ and $W_{2}$ have cross-sectional areas of $8 \times 10^{-7} \, m^{2}$ and $4 \times 10^{-7} \, m^{2}$,respectively. Masses of $20 \, kg$ and $10 \, kg$ hang from them as shown in the figure. The maximum mass $m$ that can be placed in the pan without breaking the wires is $..... \, kg$. (Use $g = 10 \, m/s^{2}$)

The property of a material which opposes the change in shape,volume,or length is called

What is the difference between a rigid body and a solid body?

Explain the spring-ball model of the elastic behavior of solids.

If the length of a string is $P$ when the tension in it is $6 \ N$ and its length is $Q$ when the tension in it is $8 \ N$, then the original length of the string is