JEE Mains · Physics · STD 11 - 7. gravitation

The acceleration due to gravity on the earth's surface at the poles is \(g\) and angular velocity of the earth about the axis passing through the pole is \(\omega .\) An object is weighed at the equator and at a height \(h\) above the poles by using a spring balance. If the weights are found to be same, then \(h\) is \(:( h << R ,\) where \(R\) is the radius of the earth)

A \(\frac{ R ^{2} \omega^{2}}{8 g }\)
B \(\frac{ R ^{2} \omega^{2}}{4 g }\)
C \(\frac{ R ^{2} \omega^{2}}{ g }\)
D \(\frac{ R ^{2} \omega^{2}}{2 g }\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(\frac{ R ^{2} \omega^{2}}{2 g }\)

Step-by-step Solution

Detailed explanation

\(g _{ e }= g - R \omega^{2}\) \(g_{2}=g\left(1-\frac{2 h}{R}\right)\) \(g_{2}=g-\frac{2 g h}{R}\) Now \(R \omega^{2}=\frac{2 g h}{R}\) \(h=\frac{R^{2} \omega^{2}}{2 g}\)

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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