Answer: The polar second moment of area (also known as the polar moment of inertia) is a property of a cross-sectional shape that describes its resistance to torsional deformation. For a hollow circular bar, the polar second moment of area (J) can be calculated using the following formula:
J = π/2 * (outer radius^4 - inner radius^4)
Given data:
Outer radius (R) = 71 mm
Inner radius (r) = 14 mm
First, we need to convert the radii to meters to have consistent units:
R = 71 mm = 71/1000 m = 0.071 m
r = 14 mm = 14/1000 m = 0.014 m
Now, we can calculate the polar second moment of area:
J = π/2 * (0.071^4 - 0.014^4)
J = π/2 * (0.0002401 - 1.952e-08)
J = π/2 * (0.00024009952)
J ≈ 3.777e-4 m^4
So, the polar second moment of area for the hollow circular bar is approximately 3.777 × 10^-4 square meters (m^4).