# Thread: Word Problem

1. ## Word Problem

A projectile is shot upwards with an initial velocity of 30m/s. Its height at time t is given by h=30t-4.9t^2. During what period of time is the projectile more than 40m above the ground? Express your answer rounded to the nearest hundredths.

2. $\displaystyle 40=30t-4.9t^2$
Use the quadratic formula.

$\displaystyle t=\frac{-30+\sqrt{900-784}}{2(-4.9}$
$\displaystyle t=\frac{2\sqrt{29}-30}{-9.8}$

$\displaystyle t=\frac{150\pm10\sqrt{29}}{49}$

$\displaystyle t_1=4.16$
$\displaystyle t_2=1.96$