A rigid bar of mass $M$ is supported symmetrically by three wires each of length $l$. Those at each end are of copper and the middle one is of iron. The ratio of their diameters, if each is to have the same tension, is equal to

A mild steel wire of length $2 L$ and cross-sectional area $A$ is stretched, well within elastic limit, horizontally between two pillars (figure ). A mass $m$ is suspended from the mid-point of the wire. Strain in the wire is

A rectangular frame is to be suspended symmetrically by two strings of equal length on two supports (figure). It can be done in one of the following three ways;

The tension in the strings will be

Consider two cylindrical rods of identical dimensions, one of rubber and the other of steel. Both the rods are fixed rigidly at one end to the roof. A mass $M$ is attached to each of the free ends at the centre of the rods.

The stress-strain graphs for two materials are shown in figure. (assume same scale)