$A$ rod of length $2 \ m$ rests on a smooth horizontal floor. If the rod is heated from $0^\circ C$ to $20^\circ C$,find the longitudinal strain developed? $(\alpha = 5 \times 10^{-5} / ^\circ C)$

The length of a metal wire is $l_1$ when the tension in it is $T_1$,and it is $l_2$ when the tension is $T_2$. The unstretched length of the wire is

$A$ wire of diameter $1\, mm$ breaks under a tension of $1000\, N.$ Another wire,of the same material as that of the first one,but of diameter $2\, mm$ breaks under a tension of ...... $N$.

$A$ metal block of mass $m$ is suspended from a rigid support through a metal wire of diameter $14\,mm$. The tensile stress developed in the wire under equilibrium state is $7 \times 10^5\,N m^{-2}$. The value of mass $m$ is $......kg$.
(Take,$g = 9.8\,m s^{-2}$ and $\pi = \frac{22}{7}$)

Which of the following statements is correct?

Why do spring balances show wrong readings of weight after they have been used for a long time?