Ratio of Time Periods for Two Planets – Rankers Physics

Keplers Law: Practice Problem & Solution

The distance of two planets from the sun are $10^{13}\text{ m}$ and $10^{12}\text{ m}$ respectively. The ratio of time periods of the planets is: (1994, 88)
$\sqrt{10}$
$10\sqrt{10}$
$10$
$1/\sqrt{10}$

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Keplers Law. Understanding the underlying formula is key to arriving at the correct answer below:

Using Kepler's 3rd Law $T^2 \propto r^3$, the ratio of time periods is $\frac{T_1}{T_2} = \left(\frac{r_1}{r_2}\right)^{3/2}$. Substituting the distances, we get $\frac{T_1}{T_2} = \left(\frac{10^{13}}{10^{12}}\right)^{3/2} = (10)^{3/2} = 10\sqrt{10}$.

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