All right. Let's get a list of kinematic equations going on here.
[tex]vf=vi+at[/tex]
[tex]vf ^{2} =vi^{2} +2ax[/tex]
[tex]x=vit+at^2/2[/tex]
What do we know?
a=gravity -9.8 m/s^2
vi=?
vf=?
x=0, since it's going up and then back down to where it started originally
t=10 s
Now, the most reasonable equation to go with would be the last one, [tex]x=vit+at^2/2[/tex].
Let's plug some things in.
[tex]0=(10)vi+(-9.8)(10)^2/2[/tex]
[tex]490=10vi[/tex]
[tex]vi=49[/tex]
Initial velocity equals 49 m/s upwards.
