We need to find the initial conditions before collision and then use the conservation of momentum to find the conditions of marble (A) after collision.
Initial Conditions:
We now find the vector components of the velocity and momentum of marble (B) after the collision.
Final Conditions:
Momentum must be conserved so we first find the y-component of marble (A)'s velocity by knowing that there is zero initial momentum in the y-direction. Then we can find the x-component by setting the initial component of p equal to the sum of the x-components of (A) and (B). The final velocity of (A) is then the resultant vector of the x and y components of velocity which is found using pythagorean's theorem.
