A $0.80\ \text{m}$ steel wire and a $1.4\ \text{m}$ brass wire are connected end to end. The joined wires are hung from a fixed support, and a force of $40\ \text{N}$ is exerted on them, as illustrated. The Young modulus of steel is $2.0 \times 10^{11}\ \text{Pa}$. The Young modulus of brass is $1.0 \times 10^{11}\ \text{Pa}$. The cross-sectional area of each wire is $2.4 \times 10^{-6}\ \text{m}^2$. Both wires obey Hooke’s law. Determine the total extension. Neglect the weight of the wires.
- A$1.7 \times 10^{-4}\ \text{m}$
- B$3.0 \times 10^{-4}\ \text{m}$
- C$3.9 \times 10^{-4}\ \text{m}$
- D$9.0 \times 10^{-4}\ \text{m}$