Related Formula
Shear modulus definition:
η = Shear StressShear Strain = (F / A)/(θ) = (F)/(Aθ)$$\eta = \frac{\text{Shear Stress}}{\text{Shear Strain}} = \frac{F / A}{\theta} = \frac{F}{A\theta}$$
where A = l · d$A = l \cdot d$ is the area of the narrow face parallel to the shearing force F$F$.
Core Logic
We are given:
Step 1: Link Modulus Terms
Express the angular deformation for each slab:
θ₁ = (F)/(l d₁ η₁)$$\theta_1 = \frac{F}{l d_1 \eta_1}$$
θ₂ = (F)/(l d₂ η₂) = (F)/(2l d₁ η₂)$$\theta_2 = \frac{F}{l d_2 \eta_2} = \frac{F}{2l d_1 \eta_2}$$
Substitute these expressions into θ₂ = 2θ₁$\theta_2 = 2\theta_1$:
(F)/(2l d₁ η₂) = 2 · ((F)/(l d₁ η₁))$$\frac{F}{2l d_1 \eta_2} = 2 \cdot \left(\frac{F}{l d_1 \eta_1}\right)$$
(1)/(2η₂) = (2)/(η₁) 4η₂ = η₁ η₂ = (η₁)/(4)$$\frac{1}{2\eta_2} = \frac{2}{\eta_1} \implies 4\eta_2 = \eta_1 \implies \eta_2 = \frac{\eta_1}{4}$$
Step 2: Solve for x
Given η₁ = 4 × 10⁹ N/m²$\eta_1 = 4 \times 10^{9}\text{ N/m}^2$:
η₂ = (4 × 10⁹)/(4) = 1 × 10⁹ N/m²$$\eta_2 = \frac{4 \times 10^9}{4} = 1 \times 10^{9}\text{ N/m}^2$$
Comparing with η₂ = x × 10⁹ N/m²$\eta_2 = x \times 10^9\text{ N/m}^2$:
x = 1$x = 1$
Pattern Recognition
Shear stress is inversely proportional to the face area parallel to the applied shearing force (A = l · d$A = l \cdot d$). Doubling the slab thickness doubles the resisting contact area, halving the applied shear stress under identical lateral loading.
Evaluation Rubric / Model Answer
1
Chapter Mix
Class 11 Physics: Mechanical Properties of Solids