How Do You Calculate the Final Velocity of Two Colliding Cars?

[rabiakhan.91]

Homework Statement

Two cars, both of mass m, collide and stick together. Prior to the collision, one car had been traveling north at speed 2v, while the second was traveling at speed v at an angle phi south of east. After the collision, the two-car system travels at speed v_final at an angle theta east of north

Find the speed v_final of the joined cars after the collision.
Express your answer in terms of v and phi.

Homework Equations

i am dividing the velocity into components using x-component and y-components of v.
vx = vcosθ
vy = vsinθ
then finding the magnitude, v = (vx^2 + vy^2)^1/2

The Attempt at a Solution

ok so my two equations are
vx = vcos and vy = 2v - vsin

after trying to find the magnitude i found the answer v(5-4sinθ)^1/2 but it says the answer is not right.
i am using θ instead of phi

 

[Angry Citizen]

There is no question in the problem statement. What do you need to find? This smells like an inelastic collision scenario requiring use of the principle of conservation of linear momentum.

 

[rabiakhan.91]

oh sorry..i have edited it

 

[Angry Citizen]

Yeah, use conservation of linear momentum as it relates to collisions. Should be in your book.