Acceleration due to Gravity — Prelims Strategy

Prelims Strategy

To effectively tackle NEET questions on Acceleration due to Gravity, a multi-pronged strategy is essential. Firstly, memorize the fundamental formula $g = GM/R^2$ and the standard value of $g \approx 9.

8\,\text{m/s}^2$(or$10\,\text{m/s}^2$if specified). Secondly, master the formulas for variations of$g$:$g_h = g/(1 + h/R_E)^2$(exact for height) and its approximation$g_h \approx g(1 - 2h/R_E)$for$h \ll R_E$; and$g_d = g(1 - d/R_E)$ for depth.

Understand when to use the exact formula versus the approximation. For conceptual questions, clearly distinguish between $g$ and $G$, and understand why $g$ is independent of the falling object's mass.

Pay close attention to the effects of Earth's rotation and shape on $g$ at the poles and equator ($g_{\text{pole}} > g_{\text{equator}}$). When solving numerical problems, always write down given values with units, identify the correct formula, substitute carefully, and perform calculations accurately.

Be wary of trap options that confuse height and depth variations or misinterpret the effect of Earth's rotation. Practice problems involving percentage changes in $g$ due to small changes in $R$, $M$, $h$, or $d$.

Visualizing the variation of $g$ from the Earth's center to outside (linear increase inside, $1/r^2$ decrease outside) can also be very helpful.