Expert: Bobby Soltani - 7/15/2005

Question
A projectile is launched straight up with an initial velocity of 112 feet per second. How long would it take it to reach 180 feet?
(Hint: use the equation h= -16.1t^2 + Vo(t) + Ho for the projectile height)

much thanks Bobby!


Answer
Hi Jeremy,

Using the given information, the initial velocity Vo is 112 ft/sec, we will assume that the initial height Ho is 0, and the final height we are solving for h is 180 ft.  So our equation looks like this:

180 = -16.1t^2 + 112t
subtract 180 from both sides
-16.1t^2 + 112t - 180 = 0
multilpy through by -1
16.1t^2 - 112t + 180 = 0
Using the quadratic formula, I get
t = 2.52, and t = 4.44

Therefore, it will initially reach 180 feet in 2.52 seconds, and then on it's way down, it will also be at 180 feet at 4.44 seconds.

Let me know if you have any questions.

Bobby