What is the Final Velocity of the 18 kg Rock After Collision in Space?

[syjxpatty]

Homework Statement

In outer space a rock with mass 4 kg, and velocity < 4000, -2800, 3400 > m/s, struck a rock with mass 18 kg and velocity < 250, -290, 260 > m/s. After the collision, the 4 kg rock's velocity is < 3600, -2300, 3900 > m/s.
What is the final velocity of the 18 kg rock?

Homework Equations

Momentum Principle

pf = pi + Fnetdeltat

The Attempt at a Solution

Please help me if you can! I am pretty frustrated with this problem and I don't know why I am getting it wrong! I used the momentum principle, but it hasnt worked since this is a collision problem. Should I use that the final speed for the 18kg rock is v2f = 2(m/M)v1i

v2 being the final velocity of 18kg
v1 being the initial velocity of 4kg

 

[Google_Spider]

Hi, Write the velocities in vector form. Like for 4 Kg rock, initial velocity will be

V_4=4000i-2800j+3400k

Then apply

P_i=P_f