Question

A person standing near the edge of a cliff 120 feet above a lake throws a rock upward with an initial speed of 40 feet per second. The height of the rock above the lake at the bottom of the cliff is a function of time and is described by the function H(t) = –16t2 + 40t + 120.
a) How many seconds will it take until the rock reaches its maximum height?
b) What is that height?

Answer 1

H(t) = -16t^2 + 40t + 120

Finding critical point...

H'(t) = -32t + 40 ...... Differentiation
0 = -32t + 40
32t = 40
t = 1.25 seconds

Thats you answer for (a). Use it to find the answer for (b).

Answer 2

Thats you...

I meant "that's your..."