Physics Q14 – NEET-UG 2026

In a solar system, the time-period of revolution of a planet tracing a circular orbit of radius

R

is proportional to :

Clue 1 of 3: Kepler's Laws of Planetary Motion

Recall the laws governing planetary motion around a star.

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Ninja Strategy•Direct Application of Kepler's Law

Directly recalling Kepler's Third Law ( $T^{2} \propto R^{3}$ ) allows for immediate identification of the correct proportionality $T \propto R^{3 / 2}$ .

🧠 Full Solution Path

Step 1: Recall Kepler's Third Law✦ Active

Kepler's Third Law of Planetary Motion states that the square of the orbital period ( $T$ ) of a planet is directly proportional to the cube of the semi-major axis ( $R$ ) of its orbit. For a circular orbit, the semi-major axis is simply the radius $R$ .

T^{2} \propto R^{3}

Step 2: Express Time Period in terms of Radius○ Expand

To find the proportionality of the time period $T$ with the radius $R$ , take the square root of both sides of the proportionality relation.

T \propto (R^{3})^{1 / 2}

T \propto R^{3 / 2}

💡 Teacher's Secret Hint

Remember that $(x^{a})^{b} = x^{a b}$ .

Step 3: Compare with Options○ Expand

The derived proportionality $T \propto R^{3 / 2}$ matches option (2).

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Physics Question 14 – NEET-UG 2026

Clue 1 of 3: Kepler's Laws of Planetary Motion

🧠 Full Solution Path