Bzzt, wrong.The force you want to know is the force exerted by the ground to change the stone's velocity back to zero when it hits. (Actually it's the reaction to that force, but Newton's Third, right?) So there is another piece of data missing: you need to know the nature of the ground the stone lands on - if it lands on mud the force will be smaller than if it landed on an expanse of concrete, because it will take longer to come to a stop, i.e. acceleration will be lower.
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Newington,
Wed 31 Mar 2004, 20:05,
archived)