The height (in m) that an object has fallen from a height of 180 m is given by the position function s(t) = -5tsquared + 180, where t > or equal to 0 and t is in seconds.
a. Find the average velocity during each of the first 2 seconds.
b. Find the velocity (instantaneous) of the object at t = 4
c. At what velocity will the object hit the ground?
I tried these, and got different answers then the correct ones. Help me out?