When a $4\, kg$ mass is hung vertically on a light spring that obeys Hooke's law, the spring stretches by $2\, cms$. The work required to be done by an external agent in stretching this spring by $5\, cms$ will be ......... $joule$       $(g = 9.8\,metres/se{c^2})$

A wire is suspended by one end. At the other end a weight equivalent to $20\, N$ force is applied. If the increase in length is $1.0\, mm,$ the ratio of the increase in energy of the wire to the decrease in gravitational potential energy when load moves downwards by $1\, mm,$ will be

A solid expands upon heating because

The elastic potential energy stored in a steel wire of length $20\,m$ stretched through $2 \,m$ is $80\,J$. The cross sectional area of the wire is $.........\,mm ^2$ (Given, $y =2.0 \times 10^{11}\,Nm ^{-2}$ )

The Young's modulus of a wire is $Y.$ If the energy per unit volume is $E$, then the strain will be

Work done by restoring force in a string within elastic limit is $-10 \,J$. Maximum amount of heat produced in the string is .......... $J$