8. The acceleration of a skydiver when air resistance builds up to be equal to half her weight is .5 m/s/s.
9a. The runners average acceleration is .5 m/s/s (average acceleration= (change in velocity)/(time interval), in this situation her change in velocity is 1 m/s and her time interval is 2 seconds).
9b. The average force is 30 Newtons. (force= mass•acceleration, where her mass is 60 kg and her acceleration is .5 m/s/s)