Starting from Newton’s law of universal gravitation, show how to find the speed of the moon in its orbit from the earth-moon distance of 3.9 × 108 m and the earth’s mass. Assume the orbit is a circle.

Respuesta :

The speed of the moon in its orbit is 1011 m/s

Explanation:

The gravitational force exerted by the Earth on the Moon is given by

[tex]F=G\frac{Mm}{r^2}[/tex]

where

[tex]G=6.67\cdot 10^{-11} m^3 kg^{-1}s^{-2}[/tex] is the gravitational constant

[tex]M=5.98\cdot 10^{24} kg[/tex] is the mass of the Earth

m is the mass of the moon

[tex]r=3.9\cdot 10^8 m[/tex] is the Earth-moon distance

This force provides the centripetal force that keeps the Moon in circular orbit, and this centripetal force is

[tex]F=m\frac{v^2}{r}[/tex]

where v is the orbital speed of the moon.

Therefore, we can equate the two forces:

[tex]G\frac{Mm}{r^2}=m\frac{v^2}{r}[/tex]

Re-arranging the equation and solving for v, we find:

[tex]v=\sqrt{\frac{GM}{r}}=\sqrt{\frac{(6.67\cdot 10^{-11})(5.98\cdot 10^{24})}{3.9\cdot 10^8}}=1011 m/s[/tex]

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