The height in meters of a projectile can be modeled by h = -4.9t^2 + vt + s where t is the time (in seconds) the object has been in the air, v is the initial velocity (in meters per seconds) and s is the initial height (in meters). A soccer ball is kicked upward from the ground and flies through the air with an initial vertical velocity of 4.9 meters per second. After how many seconds does it land approximately?

Question

terenzreignz · Answer

When it lands, what height does it have?

terenzreignz · Answer

Wrong way to phrase it...
Let me rephrase....


How high is the ball when it lands?

anonymous · Answer

4.9?

terenzreignz · Answer

When it lands, is it 4.9 meters above the ground?

anonymous · Answer

i have no idea

anonymous · Answer

what do i have to do to get the answer?

terenzreignz · Answer

Start with that... find the height of the ball as soon as it lands.  It just takes a little intuition and visualization :)

anonymous · Answer

-16

terenzreignz · Answer

So... when the ball lands, it is 16 meters underground?

anonymous · Answer

yupp

anonymous · Answer

or no 16

terenzreignz · Answer

16 means when the ball lands, it is 16 meters above the ground (in mid-air).
Does that seem reasonable?

anonymous · Answer

no.

terenzreignz · Answer

Then... what is reasonable?
When the ball lands, its height is...?

anonymous · Answer

5f

terenzreignz · Answer

What's f?

anonymous · Answer

didnt mean to put tht srry

terenzreignz · Answer

Well... you mean to tell me that when the ball *lands* it is 5 meters above the ground, then?

anonymous · Answer

omg!! i really dont kno

terenzreignz · Answer

Think... meditate... :P
Now...
how high is the ball when it LANDS...
how many meters above the ground is the ball when it LANDS...

anonymous · Answer

hmmm 0?

terenzreignz · Answer

Yes.  Finally :P

anonymous · Answer

yay!!!! that was easy lol

terenzreignz · Answer

Of course, when the ball lands, it is on the ground.
Thus, it is 0 meters above the ground.

terenzreignz · Answer

0 is not the answer. -.-

terenzreignz · Answer

that's just a stepping stone...

anonymous · Answer

oh ok wat next?

terenzreignz · Answer

We need v and s.
We already have v, the initial velocity, 4.9

terenzreignz · Answer

What's the initial height (s) ?

anonymous · Answer

4.9^2

terenzreignz · Answer

Are you guessing?
I strongly advise against it... it's too risky.

terenzreignz · Answer

And no, the initial height is not $\ 4.9^2$

anonymous · Answer

ok thnx for your help ill do the rest by myself :)
thnx

terenzreignz · Answer

Are you sure?  Well, if you're sure, post your answer here.