Projectiles in Motion!?

Question

In an archery tournament, an archer fires the arrow parallel to the horizontal with a velocity of 34 m/s. If the target is 6.00m away, how high above the bull's eye should he aim the arrow to hit the target?

and another one from the gun freak colleague!

A trench mortar fires a projectile at an angle of 30 degrees above the horizontal with velocity of 100 m/s. A soldier spots a tank travelling in the direction of the mortar at a constant rate of 3.40m/s. How far should the tank be from the mortar before the mortar is fired in order to hit the tank?

Answer 1

Time for the arrow to reach the target:

x=v*t

t=x/v

t=6/34s

As the arrow travels it drops (free fall)

y=.5*g*t^2

y=.5*9.81*(6/34)^2

Calculate y and aim y meters high above the bull's eye.