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The dimensional formula of the effective torsional constant of a spring is ________.

Asked in GUJCET 2019 · Units and dimensions

Answer: (3) M¹L²T⁻²

Step-by-step solution

Given: the torsional constant k of the suspension, defined by the restoring couple τ=kθ.

Idea: k=τ/θ, and an angle in radian is a pure number, so [k]=[τ].

A torque is τ=rF, so [τ]=L¹×M¹L¹T⁻²=M¹L²T⁻².

So [k]=M¹L²T⁻² -- the dimensions of torque, and numerically the same set as energy, with SI unit N m rad⁻¹.

Why the other options are wrong

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