50 POINTS...Which equation would best help solve the following problem? Tania releases a javelin 1.6 meters above the ground with an initial vertical velocity of 25 meters per second. How long will it take the javelin to hit the ground?

Let [tex]x(t)[/tex] be the vertical position of the javelin at time [tex]t[/tex]. Once it's thrown in the air, the only force acting on it is gravity, so the javelin would be subjected to a constant downward acceleration of approx. 9.8 meters per second per second. So

[tex]x''(t)=-9.8[/tex]

Integrating once with respect to [tex]t[/tex], we get

[tex]x'(t)=-9.8t+C_1[/tex]

where [tex]x'(t)[/tex] is the velocity of the javelin. We're told that [tex]x'(0)=25[/tex], so

[tex]25=-9.8\cdot0+C_1\implies C_1=25[/tex]

Integrating again with respect to [tex]x[/tex] to get

[tex]x(t)=-4.9t^2+25t+C_2[/tex]

and we know the javelin was initially thrown 1.6 meters above the ground, or [tex]x(0)=1.6[/tex], so we get

[tex]1.6=-4.9\cdot0^2+25\cdot0+C_2\implies C_2=1.6[/tex]

So the javelin's position at any time [tex]t[/tex] is given by

[tex]x(t)=-4.9t^2+25t+1.6[/tex]

It will hit ground when [tex]x(t)=0[/tex]. Solve this however you want; you'll find that this will happen at about [tex]t=5.165[/tex] seconds after the javelin has been thrown.