Two identical sticky masses colliding at angle φ

[Runaway]

Homework Statement

Two identical sticky masses m are moving in
the xy-plane, with their momenta at an angle
of φ with one another. They are each moving
at the same speed v when they collide at the
origin of the coordinates and stick together.
After the collision, the masses move at an
angle −θ₂ with respect to the +x axis at
speed v/2

a. pi/3
b. zero
c. 140°
d. 2pi/3
e. 110°
f. 45°

Homework Equations

p=mv
p_i=p_f

The Attempt at a Solution

I have no idea where to start

 

[vela]

There are no external forces, so you know that momentum is conserved. Start by writing the conservation of momentum equations for both the x and y directions, breaking vectors into components if necessary.