Hi! Can someone help me figure out how to solve this : The height in feet of an object is given by
y = -16t2 + 80t + 96, where y is the height and t is the time in seconds that the object is in the air.

After how much time does the object hit the ground?

Question

Hi! Can someone help me figure out how to solve this : The height in feet of an object is given by 
y = -16t2 + 80t + 96, where y is the height and t is the time in seconds that the object is in the air.

After how much time does the object hit the ground?

solomonzelman · Answer

y is the position of the subject, and t is the number of seconds.
You need find the time when it hits the ground, i.e. to find the value(s) of t when y=0.

solomonzelman · Answer

Set     $\large\color{slate}{  0=-16t^2 + 80t + 96   }$ and solve for t.

anonymous · Answer

should I use the distance formula? meh I'm confused lol

anonymous · Answer

not when you are solving a quadratic equation, no

anonymous · Answer

forget about the words, just set it equal to zero and solve 
what @SolomonZelman wrote

anonymous · Answer

oh ok I get it thank you! 'll post the answer after I solve it.

misty1212 · Answer

HI!!

solomonzelman · Answer

sure:)

anonymous · Answer

Hi ( :

misty1212 · Answer

divide all by $-16$ first, it will make it loads easier

anonymous · Answer

ah I can't see what you typed I have a "math processing error"

solomonzelman · Answer

she said that dividing the quadratic equation by -16 would make it a lot easier to solve.(divide every term in the equation by -16)

anonymous · Answer

refresh your browser, usually works

solomonzelman · Answer

btw, math process error is something that I often have. Switching browsers also works (in fact, more than refreshing, for me).

anonymous · Answer

does -2 or -3 sound right?

anonymous · Answer

as the solution set

misty1212 · Answer

no

misty1212 · Answer

$$0 = -16 (t-6) (t+1)$$

solomonzelman · Answer

no

anonymous · Answer

thanks @misty1212  I'm working on it

anonymous · Answer

1/2 or -1/8?

anonymous · Answer

@SolomonZelman  when I divided by -16 I got -t^2 + -5t + -6 = 0

anonymous · Answer

solution set of 6,-1

anonymous · Answer

but when I tried to plug it in it didn't work out

solomonzelman · Answer

$\large\color{slate}{\displaystyle 0=-16t^2 + 80t + 96}$

$\large\color{slate}{\displaystyle 0=-16(t^2 -5t -6)}$

$\large\color{slate}{\displaystyle 0=-16(t+1)(x-6)}$

solomonzelman · Answer

for t, in a quadratic equation you DO get -1 and 6, but remember, that you are finding "the seconds' because t is seconds.

solomonzelman · Answer

And you can't have -1 seconds.

solomonzelman · Answer

so, you only include the positive solution for t.

anonymous · Answer

True, thank you! :D

solomonzelman · Answer

yw