If an object is dropped from a 665-foot-high building, its position (in feet above the ground) is given by d(t)=-16t^2+665, where t is the time in seconds since it was dropped.
a. Compute d'(t). What units are associated with the derivative, and what does it measure?
b. When will the object hit the ground?
c. What is the velocity of the object when it strikes the ground (in mi/hr)?