The centripetal force is directed parallel to the string and the weight of the ball is always directed downwards. Making a force balance along the direction of vertical axis:
Fc cos 26 = W
where Fc is the centripetal force which is equal to mv2/r
W is the weight which is equal to mg
m v2 /r cos 26= mg
v2 /r cos 26 = g
v2 = rg cos 26
v2 = 2.1(9.81) cos 26
v = 4.30 m/s
The ball's speed is 4.30 m/s.
