science
posted by lesly .
If a rock has a speed of 12 m/s as it hits the ground, from what height did it fall, assuming its initial speed was zero? Its mass is 50 kg.

mass does not matter.
s = 1/2 at^2
v = at, so t = v/a
s = 1/2 a (v/a)^2 = v^2/2a = 144/19.6 = 7.3m
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