GATE-2010
26.
The Gravity value measured at the base of a 10m tall building is 40 m Gal. The value at the top of the building ignoring its mass is close
to
Solution:
Free air correction accounts for gravity variations caused by elevation
differences in the observation locations. (it does not include the
effect of mass between observed point and datum).
Δg Fa=
0.3086* h mGal
where
h is the elevation at which gravity station is above or below the
datum.
Conditions:
Correction
is ADDED for station above the datum plane.
Correction
is SUBTRACTED for station below the datum plane.
Gravity
value at the base of 10m tall building = 40 m Gal
Free air correction at the top of 10m tall building is =(0.3086 * 10) m Gal
= 3.086 m Gal.
We know that radius increase gravity decrease,
Therefore gravity at the top of the building is = 40 - 3.086 m Gal
= 36.914 m Gal
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lets practical, when you go away from center g should be decrease.
ReplyDeletein question he given value at datum plan and asking g value at 10m height.
but in real case we measure g value at some elevation and we projected that value to geoid (datum plane) ...in this process we should add FA correction to measured g value
Yes...very Nice explanation
DeleteHow is it possible.....I am not sure this
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