Moderate

The ratio of angular speed of moon around the Earth to its angular speed about its own axis is:

Correct answer: D. 1:1

  • A. 2:1
  • B. 1:6
  • C. 1:30
  • D. 1:1

Explanation

The moon orbits the Earth once every 27.322 days. In the same amount of time, the moon rotates once on its axis. As a result, the moon does not seem to be spinning but appears to observers from Earth to be keeping almost perfectly still (this is called synchronous rotation). So its angular speed (W) around its own axis isW =2π /TW(moon) = (2π)/(27.322 x 24 x 3600) = 2.67*10(-6) rad/sFor orbital motion around the earth, the angular speed isW(earth) = (2π)/(27.322 x 24 x 3600) = 2.67*10(-6) rad/sSo the ratio is 1:1

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