Finding Velocity at impact of a projectile motion with an angle

[Physics Rulez]

Homework Statement

A medieval prince trapped in a castle wraps a message around a rock and throws it from the top of the castle wall with an initial velocity of 12 m/s [42 above horizon]. The rock lands just on the far side of the castle's moat, at a level 9.5 m below the initial level. Determine the velocity at impact.

Homework Equations

finding V1y and V1x and use the pythagorean theorem to solve for the resultant velocity which will be the velocity at impact.

The Attempt at a Solution

I'm confused about how to do this question. I understand that if the rock landed on the same level as it was thrown, then i could just use the angle and initial velocity to find Vx and Vy. Then use those to solve for the resultant velocity(which would be the velocity at impact). But since the rock land blow the height it was thrown, I am confused about if i can use the same method or do i have to find the Vy(velocity of the vertical) for the bottom part of the castle as well? i tried it this way but i keep on getting the wrong answer. The sheet says that i should get an answer of 18m/s(60degrees below the horizontal).
Thanks for your help

 

[ehild]

Place the castle into a coordinate system, and write up both the x, y components of the stone and the components of velocity as functions of time. No need to separate the motion to segments above the castle and below it: it is the same y(t) function. Find the time till the stone lands at the ground and calculate the components of velocity at that time.

ehild

 

[gneill]

You might also consider using conservation of energy. The rock starts with an initial kinetic energy and potential energy due to its initial velocity and height above the ground respectively.