Help Collisions between astroids?

1. Mar 31, 2009

fball558

help!! Collisions between astroids???

1. The problem statement, all variables and given/known data

In outer space a rock with mass 6 kg, and velocity < 4200, -3100, 3000 > m/s, struck a rock with mass 18 kg and velocity < 250, -280, 360 > m/s. After the collision, the 6 kg rock's velocity is < 3700, -2500, 3500 > m/s.

What is the final velocity of the 18 kg rock? "need the x, y, and z component"

What is the change in the internal energy of the rocks? "in J"

3. The attempt at a solution
i used
P1^2 = P3^2 + P4^2 + 2P3P4cos A
where A is the angle between the particles. I did not know what A was so i assumed that it was 90 degrees like it would be in an elastic collision with identical masses, but that is a bad assumption becasue the masses are not equal.
so now im stuck. any help or a formula would be great
thanks all!!

2. Mar 31, 2009

Redbelly98

Staff Emeritus
Re: help!! Collisions between astroids???

Try writing conservation-of-momentum equations, one for each direction (x, y, and z).

3. Mar 31, 2009

fball558

Re: help!! Collisions between astroids???

ok i just did not divide by the mass at the end. i put in P instead of V

now how will i find the change in internal energy?
would i just find KE of both masses in the inital state minus the KE of both masses in the final state?

4. Apr 1, 2009

Redbelly98

Staff Emeritus
Re: help!! Collisions between astroids???

Yes.