Gravitation — NEET Exam Strategy — Summary | NoteTube

High-priority sub-topics: Variation of g (altitude vs depth comparison) and satellite orbital mechanics (velocity, period, energy) account for the majority of NEET gravitation questions. Prioritise these.

Formula recognition drills: Write

v_e = \sqrt{2gR}

,

v_0 = \sqrt{GM/r}

, and

v_e = \sqrt{2}\,v_0

from memory. These appear almost every year.

Dimensional analysis as a checker: If you are unsure of a formula, derive its dimensions.

[G] = [M^{-1} L^3 T^{-2}]

and

[g] = [L T^{-2}]

are directly asked. Dimensional consistency can eliminate wrong options in 30 seconds.

Sign discipline: Every gravitational PE formula carries a negative sign. On the answer sheet, re-read the option before marking — many 1-mark losses are from missing the minus sign.

For altitude problems with large h: Always use the exact formula

g' = gR^2/(R+h)^2

. The linear approximation will give a wrong answer for

h \geq 0.1R

.

Satellite energy trap: When a satellite moves to a lower orbit, its total energy decreases (more negative), but its kinetic energy increases and speed increases. Questions test this counter-intuitive fact.

Kepler's Third Law numericals: Express

r

in AU and

T

in years when comparing Solar System objects; this sets

4\pi^2/GM_\odot = 1

and simplifies calculation. For artificial satellites, keep SI units.

Geostationary orbit numbers to memorise:

T = 24

h,

r \approx 42{,}164

km (from centre), altitude

\approx 35{,}786

km (above surface). Both values appear in options.

Two-step escape velocity scaling: For a planet with

M' = \alpha M_E

and

R' = \beta R_E

:

v_e' = 11.2\sqrt{\alpha/\beta}

km/s. Compute the ratio first, then apply the square root — do not compute

2GM'/R'

from scratch.

Time management: Gravitation questions typically solve in 60–90 seconds with the right formula. If a problem requires more time, check whether you are using the correct formula variant (exact vs approximate altitude).