tennisball mashine shoots a ball straight up in the air, it lands after 7 seconds What's the hight of the ball given v=f(t)=30-10t
i figured that the equation i got is actually the derivative of -5t^2+30t
ball shots upp with a velocity of 30m/s, is a physics mix i have no pheta angle neede to solve it in a simpler way...vertex apex
im asked: what does 30 stand for? -10t?acceleration?
and what's max height?
i have a graf with and dowsslopping linear line crossing the y axis at 30m/s and the x axis at 3 seconds

Question

anonymous · Answer

ok tell me V=30-10t did they give you this with question

anonymous · Answer

oh ok now i can solve it

anonymous · Answer

is the answer 35 feet

anonymous · Answer

because you just sub 7 into original equation and you will get maximum height

anonymous · Answer

$$=-5(7)^{2}+30 \times 7$$

irishboy123 · Answer

yes, for $v(t) =30 - 10t$
we have 30 as initial velocity, -10 for gravity (acceleration)

so as you say $x(t) =30t - 5t^2+x_0 = 5t(6-t)+x_0$ but note the integration constant

if it lands after t = 7, then 
             $\large  x(7) =   x_0-35$ !!!!!

weird!  is the machine 35m above gound or does the ball land in a crater?!?!

anyways, at the peak of its flight $v(t) = 0 \implies 30 - 10t=0, t = 3$

solve from there