I should know how to do this.

you have a 2kg ball on 1m string. You release the ball parallel to the x axis. What is its velocity when it is pointing straight down.

I would simply apply the conservation of energy. The total gravitational potential energy lost by the ball when it reaches the bottom of the arc will be equal to the amount of kinetic energy gained.

mgh = \frac 12 mv^2

2 \cdot 9.81 \cdot 1 = \frac 12 \cdot 2 \cdot v^2

19.62= v^2

v=4.43 m/s.

Make sense?