Variation of g — Prelims Strategy

Prelims Strategy

To effectively tackle NEET questions on the variation of 'g', a multi-pronged strategy is essential. First, master the core formulas: $g_h = g(1 + h/R)^{-2}$ (and its approximation $g_h approx g(1 - 2h/R)$), $g_d = g(1 - d/R)$, and $g' = g - Romega^2 cos^2lambda$.

Understand the conditions under which the approximation for altitude is valid ($h ll R$). Second, understand the physical reasoning behind each variation. Why does 'g' decrease with height? Why does it decrease with depth?

Why is it maximum at poles and minimum at the equator? This conceptual clarity helps in answering theoretical questions and avoiding common traps. Third, practice numerical problems extensively. Pay close attention to units and ensure consistent use (e.

g., km for R and h/d). For problems involving small percentage changes, consider using differential approximations (e.g., $Delta g/g = -2Delta R/R$ or $Delta g/g = -2h/R$) as they can save time. Finally, be aware of trap options that might confuse altitude and depth variations, or misinterpret the effect of Earth's rotation.

Always identify whether the question refers to height, depth, or latitude before applying the formula.