Conservation of mechanical energy:
Down is all kinetic, when released is all potential:
1/2*m*v^2 = mgh, the initial height h = L(1-cos(alpha)) (nice to think why)
so, v^2 = 2gL(1-cos(alpha))
v = sqrt( 2gL(1-cos(alpha)) = sqrt( 2*10*2.5*(1-cos(15))
Beware of having the calculator in degrees
v = sqrt( 50* 0.0341 ) = 1.305 m/s
It is A) and they may have used 9.81 m/s^2 instead of 10 m/s^2
