Question

If a baseball is dropped from a helicopter 625 feet above ground, then its distance in feet form the ground t seconds later is modeled by -16t^2+625 How long after the ball is dropped will it hit the ground?
1.56 secs
6.25 secs
9 secs
39.06 secs
help please

Answer 1

When it hits the ground, the distance from the ground will be 0, so you have -16t^2 + 625 = 0. Can you solve for t from there?

Answer 2

so would you write it as

-16^2=-625

Answer 3

And you can try to see if 625 is a square of anything. It is the square of 25 right?

Answer 4

yea.

Answer 5

@seraphic_topaz

Answer 6

And 16 is a square of 4 right?

So from the equation above you can arrive at (4t)^2 = 25^2
And then 4t = 25; t is time and cannot be negative.
Can you solve for t from there?

Answer 7

6.25?

Answer 8

i thought you had to plug in the 60 secs.
like

4(60)=25

Answer 9

Why do you have to plug in the 60 secs?

Answer 10

since t=time i always thought you did that

Answer 11

Oh, you only need to look at the question for specification, like in this question it says "then its distance in feet form the ground *t seconds* later is modeled by -16t^2+625." Everything is in seconds so we don't need to worry about the conversion.

Answer 12

oh alright i think i got it thank you :)