Football field goal trajectory using completing the square

[night_stroller]

hi,

Can somebody please help me solve this through completing the square?

A football player attempts a field goal by kicking the football. The ball follows the path modeled by the equation h=-4.9^2+10t+3, where h is the height of the ball above the ground in metres, and t is the time since the ball was kicked in seconds.

a) Describe the path of the ball.
b) After how many seconds does the ball reach the ground?
c) The ball must clear the uprights for the field goal to count. The uprights are approximately 5m high. How long does the ball stay above 5 m in height?

 

[quantumdude]

Must you do it by completing the square? Why not use the quadratic formula?

 

[Werg22]

We should have a mod roll call.

 

[night_stroller]

Must you do it by completing the square? Why not use the quadratic formula?

I haven't learned it yet.

 

[Gib Z]

I haven't learned it yet.

Why not prove it then =] ? Completet the square on the general quadratic form $ax^2 + bx + c$, where a, b and c are real constants.

 

[Trail_Builder]

which bit are you stuck on exactly?

for a), its kind of you know it or you dont.

for b), when the ball hits the ground, you know its height is what?

from there you can simply solve the quadratric using the quadratic formula (be useful if you can derive it, but just search google if you can't be bothered).

for c), same sort of method as b), just use a dif value for height.

need any more help?