Uniform accelerated motion problem help

[DB]

im stuck on this one:

a person standing on an overpass above a roadway wishes to drop something onto a truck. the truck starts from rest and accelerates at half the speed of gravity from a position 100 m from the point of impact. the overpass is 30 m above the truck. how long after the truck started should the person wait before dropping the packgage? (gee = 10 m/s^2)

okay so basicallly wat I've got is this: the truck will take 20 seconds until it is perfectly lined up with the overpass;that being the point of impact. i also got that it will take 2.5 seconds for the package to travel 30 m accelerating at gee.

the answer is approx 3.9 secs but i don't know how to come to this, have i done something wrong?

 

[Fermat]

...
okay so basicallly wat I've got is this: the truck will take 20 seconds until it is perfectly lined up with the overpass...

There's your error.
Check your arrithmetic again. Didi you use the correct formula ?
I got Δt = 3.87 sec

 

[hypermorphism]

Note that if the person drops the package when the truck is directly beneath them, the package will hit the ground long after the truck has passed. You need to drop it a certain amount of time before the truck reaches directly beneath you. Also, your time for the truck to reach you is too high (remember, it is accelerating).