posted by jawn .
At what altitude above the Earth's surface is the acceleration due to gravity equal to g/128?
then solved for r and got 72080960. its within 10% of the correct answer but not correct. what am i doing wrong? (ive already rounding differently,etc)
you need to subtract earth radius from r, the question asked for altitude.
There was a easier way to do this.
g/128=g*(re/(re+alt))^2 notice the g's divide out, or
or (1+alt/re )^2=128
take the sqrt of each side...
alt= re * (sqrt128 -1)
Now you see why your answer was within ten percent, as the sqrt 128 is about 11.