Imagine a planet of mass M with a small moon of mass m and radius a orbiting it and keeping the same face toward it.If the moon now approaches the planet.there will be a critical distance from the planet's center at which loose material lying on the moon's surface will be lifted off.Show that this distance is given by r=a(3M/m)^(1/3). 这题是在讲当月球一直靠进行星到某个距离时,表面上的物质会开始脱离,应该是因为 地球的万有引力和月球的万有引力互相抵消了使得向心力不足? 想了一整天都想不出来,对地球同一面的条件也不会用 恳请大大出手相助吧QQ --

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