Approximately One Billion Years Ago, the Moon Orbited the Earth

Multiple Choice

Approximately one billion years ago, the Moon orbited the Earth much closer than it does today. The radius of the orbit was only 24 400 km. The orbital period was only 23 400 s. Today, the average radius is 385 000 km; and the present period is 2.36 × 10⁶ s. Assuming that the orbit of the Moon is circular, calculate the ratio of the speed of the Moon in its ancient orbit to the speed that it has today.

A) 15.8
B) 12.8
C) 10.2
D) 7.15
E) 6.39