The acceleration due to gravity on the Earth's
surface is g. If R is the
radius of the Earth, what
is the acceleration due to
gravity at a height 2R above
the Earth?

Lexy is correct because angle r is between the incident wave,  n  = 0, and a diffracted wave.

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.

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