The torsional stiffness k is given by the relation (where G is rigidity modulus, J is polar moment of inertia and l is length.)
- Ak = GJ / lCorrect
- Bk = Gl / J
- Ck = lJ / G
- Dk = GJ / l²
Solution
Concept
Torsional stiffness
Formula
k = T / θ = G J / l
Step-by-step solution
1. T / J = G θ / l. 2. T / θ = G J / l.
Explanation
Torsional stiffness is the torque needed for a unit angle of twist.
Why the other options are wrong
The other expressions do not follow from the torsion equation.
Shortcut
k = GJ/L.
Common mistake
Dividing by l².
Correct answer: A) k = GJ / l