Which of the following graphs correctly depicts the spring constant $k$ versus the length $l$ of the spring?

$A$ wire of cross-sectional area $3 \, mm^2$ is first stretched between two fixed points at a temperature of $20^{\circ}C$. Determine the tension in the wire when the temperature falls to $10^{\circ}C$. Given: Coefficient of linear expansion $\alpha = 10^{-5} \, ^{\circ}C^{-1}$ and Young's modulus $Y = 2 \times 10^{11} \, N/m^2$.

In nature,the failure of structural members usually results from large torque because of twisting or bending rather than due to tensile or compressive strains. This process of structural breakdown is called buckling. In cases of tall cylindrical structures like trees,the torque is caused by their own weight bending the structure,such that the vertical line through the centre of gravity does not fall within the base. The elastic torque caused by this bending about the central axis of the tree is given by $\frac{Y\pi r^4}{4R}$,where $Y$ is the Young's modulus,$r$ is the radius of the trunk,and $R$ is the radius of curvature of the bent surface along the height of the tree containing the centre of gravity (the neutral surface). Estimate the critical height of a tree for a given radius of the trunk.

If the temperature of a wire of length $2 \,m$ and area of cross-section $1 \,cm^2$ is increased from $0^{\circ}C$ to $80^{\circ}C$ and is not allowed to increase in length,then the force required for it is ............$N$ $\{Y=10^{10} \,N/m^2, \alpha=10^{-6}/^{\circ}C\}$

Overall changes in volume and radii of a uniform cylindrical steel wire are $0.2 \%$ and $0.002 \%$ respectively when subjected to some suitable force. Calculate the longitudinal tensile stress acting on the wire. (Given: Young's modulus $Y = 2.0 \times 10^{11} \ N/m^2$)

The correct increasing order for the modulus of elasticity for copper,steel,glass,and rubber is: