A cuboidal block of sides a, b and c is fixed on ground. The top is pushed by a horizontal force F as shown. The angle φ by which the block deforms is : (η is modulus of rigidity)
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A cuboidal block of sides a, b and c is fixed on ground. The top is pushed by a horizontal force F as shown. The angle φ by which the block deforms is : (η is modulus of rigidity)

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 C: F/(bcη). Therefore the correct answer is C.