A model rocket is shot upward from the earths surface with a

A model rocket is shot upward from the earth\'s surface with an initial velocity of 45 ft/sec. How many seconds will it take the object to reach a height of 30 ft the first time? Use the formula h = vt - 16t^2 and round your answer to the nearest tenth of a second. _______ seconds

Solution

h(t) = vt - 16t^2
intial velocity , v = 45ft/sec

So, h(t) = 45t - 16t^2

height h(t) = 30 ft

So, 30 = 45t - 16t^2

-16t^2 + 45t - 30 =0

solve using quadratic formula:

t = [ -45 +/- sqrt( 45^2 - 4*16*30)]/-32

t = 1.08 = 1.1 sec ; t2 = 1.72 = 1.7 sec

So, t = 1.1 sec (solution)