projectile

**william** · March 9th 2009, 01:33 PM

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 then $40m$ above the ground? express your answer rounded to the nearest hundredths

my thinking: $40=30t-4.9t^2$ but can't go anywhere from there

**JeWiSh** · March 9th 2009, 01:42 PM

Originally Posted by william

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 then $40m$ above the ground? express your answer rounded to the nearest hundredths

my thinking: $40=30t-4.9t^2$ but can't go anywhere from there