A 2.5 kg stone is released from rest and falls toward earth. After 4s, the magnitude of its momentum is:

Question

My work:
J=F*t
=(F *t)= 24.5N * 4s
F= 2.5 *9.81= 24.5
J=P
P= 98kg m/s

A sphere X, of mass 2kg, is moving to the right at 10m/s. Sphere Y, of mass 4 kg is moving to the left at 10m/s. The two sphere collide head on. The magnitude of the impulse of X and Y is:
Would the answer be half the magnitude of the impulse of Y on X because Y is two times greater in mass then X.

Yes on the first one.
One the second, remember that impulse is a vector, these vectors are in the opposite direction. You are correct, 20 kg*m/s to the left.