## babydoll332 Group Title A projectile is thrown upward so that its distance above the ground after t seconds is h = - 16t2 + 440t. After how many seconds does it reach its maximum height? one year ago one year ago

1. Outkast3r09 Group Title

few ways to solve this

2. completeidiot Group Title

are you familiar with derivatives?

3. babydoll332 Group Title

with a graph correct?

4. Outkast3r09 Group Title

Without Calculus y|dw:1349657074734:dw|ou know that this graph will look like this

5. babydoll332 Group Title

oh ok

6. Outkast3r09 Group Title

so you know it hits its maximum height at its' vertex. you know how to find the x for the vertex by $x=\frac{-b}{2a}$

7. Outkast3r09 Group Title

x so happens to be time in our case =P

8. babydoll332 Group Title

ohhhh

9. Outkast3r09 Group Title

|dw:1349657191197:dw|

10. babydoll332 Group Title

21 seconds

11. Outkast3r09 Group Title

with calculus $y=-16t^2+440t$ $y'=-32t+440=velocity$ we know that the velocity of y is 0 at the point of max height so $0=-32t+440$ $-440=-32t$ $\frac{-440}{-32}=t$ 13.75 seconds

12. Outkast3r09 Group Title

without calculus $ax^2+bx+c$ in our case $ax^2+bx$ $x=\frac{-b}{2a}$ $\frac{-440}{-32}$ 13.75 seconds

13. babydoll332 Group Title

oh wow i was completly of thanks alot !!!