(a) These are stress-strain curves for three different materials, $\mathrm{P},\mathrm{Q} \& \mathrm{R}$. State and explain which material has the greatest Young modulus.

State the meaning of tensile stress and tensile strain.

(b) A vertical steel wire of length $1.6 \mathrm{m}$ and cross-sectional area $1.3\times {10}^{-6}{ \mathrm{m}}^2$ carries a weight of $60 \mathrm{N}$. The Young modulus for steel is $2.1\times {10}^{11} \mathrm{Pa}$. Calculate: stress.

A vertical steel wire of length $1.6 \mathrm{m}$ and cross-sectional area $1.3\times {10}^{-6}{ \mathrm{m}}^2$ carries a weight of $60 \mathrm{N}$. The Young modulus for steel is $2.1\times {10}^{11} \mathrm{Pa}$. Calculate the stress in the wire.

(b) A vertical steel wire of length $1.6 \mathrm{m}$ and cross-sectional area $1.3\times {10}^{-6}{ \mathrm{m}}^2$ carries a weight of $60 \mathrm{N}$. The Young modulus for steel is $2.1\times {10}^{11} \mathrm{Pa}$. Calculate:

(ii) The strain in the wire

(b) A vertical steel wire of length $1.6 \mathrm{m}$ and cross-sectional area $1.3\times {10}^{-6}{ \mathrm{m}}^2$ carries a weight of $60 \mathrm{N}$. The Young modulus for steel is $2.1\times {10}^{11} \mathrm{Pa}$. Calculate:

(iii) The extension produced in the wire by the weight.

To allow for expansion in the summer when temperatures rise, a steel railway line laid in cold weather is pre-stressed by applying a force of $2.6\times {10}^5 \mathrm{N}$ to the rail of cross-sectional area $5.0\times {10}^{-3}{ \mathrm{m}}^2$ If the railway line is not pre-stressed, a strain of $1.4\times {10}^{-5}$ is caused by each degree Celsius rise in temperature. The Young modulus of the steel is $2.1\times {10}^{11} \mathrm{Pa}$.

(a) State and explain whether the force applied to the rail when it is laid should be tensile or compressive.

To allow for expansion in the summer when temperatures rise, a steel railway line laid in cold weather is pre-stressed by applying a force of $2.6\times {10}^5 \mathrm{N}$ to the rail of cross-sectional area $5.0\times {10}^{-3}{ \mathrm{m}}^2$ If the railway line is not pre-stressed, a strain of $1.4\times {10}^{-5}$ is caused by each degree Celsius rise in temperature. The Young modulus of the steel is $2.1\times {10}^{11} \mathrm{Pa}$.

(b) Calculate:

(i) The strain produced when the rail is laid

To allow for expansion in the summer when temperatures rise, a steel railway line laid in cold weather is pre-stressed by applying a force of $2.6\times {10}^5 \mathrm{N}$ to the rail of cross-sectional area $5.0\times {10}^{-3}{ \mathrm{m}}^2$ If the railway line is not pre-stressed, a strain of $1.4\times {10}^{-5}$ is caused by each degree Celsius rise in temperature. The Young modulus of the steel is $2.1\times {10}^{11} \mathrm{Pa}$.

(b) Calculate:

(ii) The temperature rise when the rail becomes unstressed.