Two wires are made of the same material and have the same volume. The first wire has cross-sectional area $A$ and the second wire has cross-sectional area $3A$. If the length of the first wire is increased by $\Delta l$ on applying a force $F$, how much force is needed to stretch the second wire by the same amount?

In steel, the Young's modulus and the strain at the breaking point are $2 \times {10^{11}}\,N{m^{ – 2}}$ and $0.15$ respectively. The stress at the breaking point for steel is therefore

Two exactly similar wires of steel and copper are stretched by equal forces. If the total elongation is $2 \,cm$, then how much is the elongation in steel and copper wire respectively? Given, $Y_{\text {steel }}=20 \times 10^{11} \,dyne / cm ^2$, $Y_{\text {copper }}=12 \times 10^{11} \,dyne / cm ^2$

A composite rod made up of two rods $AB$ and $BC$ are joined at $B$ . The rods are of equal length at room temperature and have equal masses. The coefficient of linear expansion a of $AB$ is more than that of $BC$. The composite rod is suspended horizontal by means of a thread at $B$. When the rod is heated

A wooden wheel of radius $R$ is made of two semicircular part (see figure). The two parts are held together by a ring made of a metal strip of cross section area $S$ and length $L$. $L$ is slighly less than $2\pi R$. To fit the ring on the wheel, it is heated so that its temperature rises by $\Delta T$ and it just steps over the wheel.As it cools down to surronding temperature, it presses the semicircular parts together. If the coefficint of linear expansion of the metal is $\alpha$, and its young's modulus is $Y$, the force that one part of wheel applies on the other part is