## allie_bear22 2 years ago 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?

1. terenzreignz

When it lands, what height does it have?

2. terenzreignz

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

3. allie_bear22

4.9?

4. terenzreignz

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

5. allie_bear22

i have no idea

6. allie_bear22

what do i have to do to get the answer?

7. terenzreignz

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

8. allie_bear22

-16

9. terenzreignz

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

10. allie_bear22

yupp

11. allie_bear22

or no 16

12. terenzreignz

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

13. allie_bear22

no.

14. terenzreignz

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

15. allie_bear22

5f

16. terenzreignz

What's f?

17. allie_bear22

didnt mean to put tht srry

18. terenzreignz

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

19. allie_bear22

omg!! i really dont kno

20. terenzreignz

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

21. allie_bear22

hmmm 0?

22. terenzreignz

Yes. Finally :P

23. allie_bear22

yay!!!! that was easy lol

24. terenzreignz

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

25. terenzreignz

0 is not the answer. -.-

26. terenzreignz

that's just a stepping stone...

27. allie_bear22

oh ok wat next?

28. terenzreignz

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

29. terenzreignz

What's the initial height (s) ?

30. allie_bear22

4.9^2

31. terenzreignz

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

32. terenzreignz

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

33. allie_bear22

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

34. terenzreignz