I need Help. Rotational Kinetic Energy of Earth and the Moon.

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SUMMARY

The discussion focuses on calculating the ratio of the rotational kinetic energy of the Earth to that of the Moon. Key parameters include the mass of the Earth (5.97 × 1024 kg), the radius of the Earth (6.37 × 106 m), the mass of the Moon (7.35 × 1022 kg), and the radius of the Moon (1.74 × 106 m). The formula for kinetic energy (KE = (1/2)(moment of inertia)(angular velocity)) is established, with the moment of inertia for a sphere given as I = (2/5)MR2. The angular velocity for the Earth can be derived from its 24-hour rotation period, while the Moon's rotation period must also be determined.

PREREQUISITES
  • Understanding of rotational kinetic energy and its formula
  • Knowledge of moment of inertia for spherical objects
  • Familiarity with angular velocity calculations
  • Basic concepts of celestial mechanics and rotation periods
NEXT STEPS
  • Calculate the angular velocity of the Earth using its 24-hour rotation period
  • Determine the angular velocity of the Moon based on its rotation period
  • Compute the moment of inertia for both the Earth and the Moon
  • Divide the calculated rotational kinetic energies to find the ratio
USEFUL FOR

Students studying physics, particularly those focusing on rotational dynamics, as well as educators and anyone interested in celestial mechanics and energy calculations.

maxgotsrice
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Homework Statement



What is the ratio of the rotational kinetic energy of the Earth to the rotational kinetic energy of the Moon as they spin about their axes?

The Attempt at a Solution




Me = Mass of Earth (5.97 × 1024 kg)
Re = Radius of Earth (6.37 × 106 m)
Mm = Mass of Moon (7.35 × 1022 kg)
Rm= Radius of Moon (1.74 × 106 m)

this is all i know I don't know where to start. I know KE=(1/2)(moment of inertia)(angular velocity)
 
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The moment of inertia for a sphere is
I = \frac{2}{5}MR^2

And you can find the angular velocity for the Earth because you know it has a period of one day. I think you'll have to find the length of a day on the moon.

After that just divide the two energies, you've got the right equation and all the rest of the right info though.
 

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