The material which practically does not show elastic after effect is

$A$ wire of length $40 \text{ cm}$ is stretched by $0.1 \text{ cm}$. The strain on the wire is

One end of a uniform rod of mass $m_1$ and cross-sectional area $A$ is hung from a ceiling. The other end of the rod is supporting a mass $m_2$. The stress at the midpoint of the rod is:

$A$ lift of mass $1600 \text{ kg}$ is supported by a thick iron wire. If the maximum stress which the wire can withstand is $4 \times 10^8 \text{ N/m}^2$ and its radius is $4 \text{ mm}$, then the maximum acceleration the lift can take is . . . . . . $\text{m/s}^2$. (Take $g = 10 \text{ m/s}^2$ and $\pi = 3.14$)

If under an external force,a change in length $\Delta l$ occurs in a rod of original length $l$,then write the formula for longitudinal strain.

Why is rubber used to make cycle seats instead of wood or iron?