Each of the three blocks P, Q and R shown in figure has a mass of 3 kg. Each of the wires A and B has cross-sectional area 0.005 cm² and Young's modulus 2 ×10¹¹ N m⁻². Neglect friction. Find the longitudinal strain developed in each of the wires. Take g = 10 m s⁻². Which of the following gives the correct final result?
Options

Question

Each of the three blocks P, Q and R shown in figure has a mass of 3 kg. Each of the wires A and B has cross-sectional area 0.005 cm² and Young's modulus 2 ×10¹¹ N m⁻². Neglect friction. Find the longitudinal strain developed in each of the wires. Take g = 10 m s⁻². Which of the following gives the correct final result?

Options

G1 Physics · Accepted Answer

Use stress σ=F/A, strain ε=ΔL/L and Young's modulus Y=σ/ε. For a uniform segment, ΔL=FL/(AY); for thermal restraint, thermal strain αΔT produces stress YαΔT. Evaluating the given data/statements gives strain A=1×10⁻⁴; strain B=2×10⁻⁴. Therefore the correct answer is A.