Suppose this firework is set to explode 3 seconds after it is launched. At what height will this firework be when it explodes?

Question

My equation is h(t)=-16t^2+120t+20
How do I do this?

Answer 1

h = 20 + 120 * 3 - 16 (9)

= 20 + 360 - 144

in feet where g = 32 ft/s^2

Answer 2

this is because in feet and seconds
acceleration of gravity, g = 32 ft/s^2

then velocity v = Vi - g t
where Vi is initial velocity and g = 32 ft/s^2

and height h is
h = Hi + Vi t - (1/2)g t^2
in this problem
h = Hi + Vi t - 16 t^2
where Hi = 20 and Vi = 120

Answer 3

Thanks Damon!

Answer 4

You are welcome.