A vessel at rest explodes, breaking into three pieces. Two pieces, having equal mass, fly off perpendicular to one another with the same speed of 90 m/s. One goes along the negative x-axis and the other along the negative y-axis. The third piece has three times the mass of each other piece. What are the direction and magnitude of its velocity immediately after the explosion? a) What is the angle with respect to the x-axis?

b)What is the magnitude of its velocity?

for A) I understand that the value is 45 degrees however I do not exactly understand why it is 45 degrees. and for B) I have no idea where to start...I know that momentum is involved but thats about it.

2. P=mv ? not sure where to go from there.