41 Height estimate The distance an object falls when released from rest under the influence of Earth s gravity and with no air resis tance is given by d t 16r where d is measured in feet and t is measured in seconds A rock climber sits on a ledge on a verti cal wall and carefully observes the time it takes for a small stone to fall from the ledge to the ground a Compute d t What units are associated with the derivative and what does it measure b If it takes 6 s for a stone to fall to the ground how high is the ledge How fast is the stone moving when it strikes the ground