text: a  30.0n stone is dropped from a height of 10.0m and strikes the ground with a velocity of 7.00m/s. what avera i am doing physics i. i would need to know the average force of air friction as it acts on it as it falls? this is not question of phys. i.  you must to use this:  f = ma -bv, wher b is a coeffient of friction and v is the velocity. you must to know the coefficient b and resolved the differential equation...  -bv is the "force air"