Question

If an object is dropped from a height of 144 feet, the function h(t)=-16t^2+144 gives the height of the object after t seconds. When will the object hit the ground?

Answer 1

what is the height of the object from the ground if the object is on the ground?

Answer 2

0.

Answer 3

If the object is on the ground? I think it is 0 feet above the ground.

Answer 4

right! h=0

Answer 5

\[0=-16t^2+144\]

Answer 6

So t is time
t is the when that you are solving for

Answer 7

how do you solve for t?

Answer 8

\[0=-a^2+b\]
If we wanted to solve this for a
\[\text{I would add }a^2 \text{ on both sides}\]
\[a^2=b\]
Then I would take square root of both sides
\[a=\pm \sqrt{b}\]

Answer 9

So for your equation what would you add to both sides?

Answer 10

9 seconds?

Answer 11

\[9=t^2 ?\]

Answer 12

is that what you are saying?

Answer 13

you didn't do anything with the square part yet have you?

Answer 14

\[\approx\]0.9083, -9.9083

Answer 15

\[h(t)=-16t^2+144\]
This is the function right?
Now we want to know what t is when h is 0
\[0=-16t^2+144\]
\[\text{ add } 16t^2 \text{ on both sides } \]
\[16t^2=144 \]

Answer 16

Divide both sides by 16 to undo the multiplication of 16
(Or in other words multiply both sides by 1/16)

Answer 17

so 9 is correct.

Answer 18

nope

Answer 19

\[t^2=\frac{144}{16}\]
\[t^2=9\]

Answer 20

Do you know what to do from here?