# P the Moon Takes About 27.3 Days to Revolve Round the Earth in a Nearly Circular Orbit of Radius 3.84 × 105 Km/ Calculate the Mass of the Earth from These Data. - Physics

Sum

The moon takes about 27.3 days to revolve round the earth in a nearly circular orbit of radius 3.84 × 105 km/ Calculate the mass of the earth from these data.

#### Solution

Time period of rotation of the Moon around the Earth is given by $T = 2\pi\sqrt{\frac{r^3}{GM}}$

where r is the distance between the centres of the Earth and Moon and m is the mass of the Earth.

$Now, 27 . 3 = 2 \times 3 . 14\sqrt{\frac{\left( 3 . 84 \times {10}^5 \right)^3}{6 . 67 \times {10}^{- 11} M}}$

$\Rightarrow 27 . 3 \times 27 . 3 = \frac{2 \times 3 . 14 \times \left( 3 . 84 \times {10}^5 \right)^3}{6 . 67 \times {10}^{- 11} M}$

$\Rightarrow M = \frac{2 \times \left( 3 . 14 \right)^2 \times \left( 3 . 84 \right)^3 \times {10}^{15}}{3 . 335 \times {10}^{- 11} \times \left( 27 . 3 \right)^2}$

$= 6 . 02 \times {10}^{24} kg$

∴ The mass of the Earth is found to be 6.02× 1024 kg.

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#### APPEARS IN

HC Verma Class 11, 12 Concepts of Physics 1
Chapter 11 Gravitation
Q 30 | Page 227