Question

A stone is thrown vertically upward from a platform that is 21 feet above ground at a rate of 90 feet per second. Use the projectile formula

h
=
−
16
t
2
+
v
0
t
+
h
0
to find how long it will take the stone to reach its maximum height, and then find the maximum height the stone reaches. [Recall that
v
0
is the initial velocity of the object and
h
0
is the inital height of the object.]

Answer: The stone reaches its maximum height after
0
Incorrect
seconds
Correct. The maximum height the stone reaches is

feet

Answer 1

h(t) = -16t² + 90t

h'(t) = -32t + 90 = 0

t = 45/16 = 2.81 seconds

The stone reaches its maximum height after 2.81 seconds.

h(45/16) = -16(45/16)² + 90(45/16)

= 126.56 feet

The maximum height the stone reaches is 126.56 feet.