[問題] 一道功與能的問題
Humans currently use energy at the rate of about 10^13 W .
Suppose a future inventor finds a way to extract usable energy
from the moon's orbital motion and beam that energy,without
loss,to earth.If our energy use remains constant,by how much
will the radius and period of the moon's orbit decrease after
its energy has been tapped for 100 years?Give your answers as
numerical values and as a percentage decrease.
這是我家教學生的問題，他在美國讀高中。
題目前半段的意思我看得很模糊，也不太清楚他要問什麼。
可以請板上的物理同好幫忙思索一下如何解題嗎？
這題的答案是
317m and 2.9s
感謝
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