(a) A parachute creates enough air resistance to keep the downward speed of an 80-kg sky diver to a constant 6.0 m/s. Assuming that the force of air resistance is given by f = bv², calculate b for this case. 

(b) A sky diver free-falls until his speed is 60 m/s before opening his parachute. If the parachute opens instantaneously, calculate the initial upward force exerted by the chute on the sky diver moving at 60 m/s. Explain why it is important that the parachute takes a few seconds to open.