Question

David drops a ball from the top of a building with a height of 64 feet.

The height (h) of the ball, in feet, after (t) seconds can be found using
the formula h=-16° +64. How long will it take the ball to reach the
ground?
A)3 sec
B)2sec
C)1 sec
D)none

Answer 1

Explanation:

The position formula for this is actually

`s(t)=-16t^2+64`

It says, in not so may words, that the object was dropped under the influence of gravity from a height of 64 feet. When it hits, the ground, it will not be above ground at all anymore...it will be ON the ground and have a height of 0. Therefore, if we set the position function equal to 0 and solve for t, we are finding out how long it will take for the object to hit the ground.

`0=-16t^2+64` and

`16t^2=64` and

`t^2=4` and

t = 2

It takes 2 seconds for the object to hit the ground from 64 feet up.