Question

Consider two flat parallel plates placed in horizontal condition 1.2 cm apart and the space between them is filled with the oil of viscosity 15.0 poise. The upper plate is moved with a velocity of 3.25 m/s, then the shear stress in the oil is
1. Between 100 - 150 N /m²
2. Between 151 - 200 N/m²
3. Between 201 - 350 N/m²
4. Between 351 - 450 N/m²

Answer 1

Correct Answer - Option 4 : Between 351 - 450 N/m²

Concept:

Shear stress in the oil

\(τ = μ \times \frac {∂ V}{∂ y}\)

where: μ = Dynamic viscosity, τ = Shear stress, V = velocity of plate, y = distance between the plates.

Calculation:

Given:

Thickness = t = 1.2 cm = 0.012 m, μ = 15 poise = 1.5 Ns/m², ΔV = 3.25 m/s

\(τ = μ \times \frac {∂ V}{∂ y}\)    \(τ = μ \times \frac {Δ V}{t}\) 

\(τ = 1.5\times \frac {3.25}{0.012} = 406.25~N/m^2\)