Mechanical Properties of solids NCERT Solutions Class 11 Physics - Solved Exercise Question 9.6

Question 9.6:

The edge of an aluminium cube is 10 cm long. One face of the cube is firmly fixed to a vertical wall. A mass of 100 kg is then attached to the opposite face of the cube. The shear modulus of aluminium is 25 GPa. What is the vertical deflection of this face?

Solution:

Edge of the aluminium cube, L = 10 cm = 0.1 m
The mass attached to the cube, m = 100 kg
Shear modulus (η) of aluminium = 25 GPa = 25 × 10⁹ Pa
Shear modulus, η = Shear stress / Shear strain  =  (F/A) / (L/ΔL)
Where,
F = Applied force = mg = 100 × 9.8 = 980 N
A = Area of one of the faces of the cube = 0.1 × 0.1 = 0.01 m²
ΔL = Vertical deflection of the cube
∴ ΔL = FL / Aη
= 980 X 0.1 / [ 10^-2 X (25 X 10⁹) ]
= 3.92 × 10^–7 m
The vertical deflection of this face of the cube is 3.92 ×10^–7 m.