long question, help needed!

• January 1st 2009, 08:48 AM
14041471
long question, help needed!
This is a long question whilch i think involves the quadratic formula, but i generally dont know where to start with this so any help would be much appreciated.

"In an engineering test, a rocket sled is propelled into a target. The sled’s distance d in meters from the target is given by the formula d = -1.5t^2 + 120 where t is the number of seconds after rocket ignition. How many seconds have passed since rocket ignition when the sled is 10 meters from the target?"
• January 1st 2009, 09:06 AM
skeeter
you are given $d = 10$ ...

$10 = -1.5t^2 + 120$

$1.5t^2 = 110$

$t^2 = \frac{220}{3}$

since $t > 0$ ...

$t = \sqrt{\frac{220}{3}}$