Subterranean Perihelion

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88.Subterranean Perihelion

+10

A small mote at distance

R

from the center of a uniform-density spherical planet of mass

M

and radius

R_P

(with

R < R_P

) experiences only the planet's gravity. At an instant when its motion is purely tangential with small speed

v

, what is the closest subsequent approach to the planet's center?

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