Question

Two disks are on a frictionless plane as shown. The first disk, with mass M is initially at rest. The second disk with mass 2M has an initial velocity of 6 m/s in the y direction before colliding with the first disk. After the collision, the disk with mass 2M is deflected 15° (deflected to the left) and has speed 3 m/s. (Ignore the effects of gravity, all the pieces are moving in a horizontal plane, and you may neglect friction). What is the x component of the velocity of disk 1(deflected to the right) (mass M) after the collision?

Answer 1

IT is much to complicated to work out here.
worke it this way:
conservation of momentum in x direction
conservation of momentum in y direction

conservation of energy.
That should give you all you need.