COMEDK · Physics · 2. Units and Dimensions

If units of mass, length and gravitational constant are chosen to fundamental units, the dimensions of time would be

A \(\mathrm{M}^{-1 / 2} \mathrm{~L}^{3 / 2} \mathrm{G}^{-1 / 2}\)
B \(\mathrm{M}^{1 / 2} \mathrm{~L}^{1 / 2} \mathrm{G}^{-1 / 2}\)
C \(\mathrm{M}^{-1} \mathrm{~L}^3 \mathrm{G}^{-1}\)
D \(\mathrm{M}^1 \mathrm{~L}^{1 / 2} \mathrm{G}^2\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(\mathrm{M}^{-1 / 2} \mathrm{~L}^{3 / 2} \mathrm{G}^{-1 / 2}\)

Step-by-step Solution

Detailed explanation

The dimension of the gravitational constant \(G\) is given by the formula \(F = G \dfrac{m_1 m_2}{r^2}\), which implies \([G] = \dfrac{[F][r^2]}{[m^2]} = \dfrac{MLT^{-2} L^2}{M^2} = M^{-1} L^3 T^{-2}\). We express time \(T\) in terms of mass \(M\), length \(L\), and…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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