velocity

how are you getting it?

use relative velocity concept.
suppose the left wedge is at rest.
then calculate remaining velocities
finally convert it to velocity w.r.t. ground

Just Exaggerating what Aditya Said :

Sit on the Wedge L (for Left) and Observe: You see that the R (for Right) Wedge is moving away with the velocity ' 3u ' m/s. Now resolving this velocity along the incline and then along the x-y axes, we can get the velocity of the sphere as :

V _sa = 3u i - 3√u j

Coming back to the ground frame, Va = - u i

So V _sg = V _{s L} + V _L

Putting we have V _sg = 2u i - √3 u j => | V _sg | = √7 u

Notations : sg - Sphere w. r .t ground | l - Wedge L

correct.