An object is dropped from the top of a 100-m tower. Its height above the ground after 1 sec is 100-4.9t^2 m. How fast is it falling 2 sec after it is dropped?
lim as h--> 0 (f(t+h)- f(t))/h
or as an easier formula, I think.
lim as h--> 0(f(t) - f(h))/(t-h)
Guess: 100=4.9t^2 m goes as t and solve. Then plug in 2 for t.