What are the velocities of the particles after a perfectly inelastic collision?

[cse63146]

Homework Statement

Particle 1 has initial velocity v, directed to the right, and particle 2 is initially stationary.
Let the mass of particle 1 be m and the mass of particle 2 be 3m. If the collision is perfectly inelastic, what are the velocities of the two particles after the collision?

Homework Equations

$$m_{}1$$$$v_{}1$$ + $$m_{}2$$$$v_{}2$$= ($$m_{}1$$+$$m_{}2$$)v

The Attempt at a Solution

$$m_{}1$$$$v_{}1$$ = (m + 3m)v
$$v_{}1$$ = ((4m)v)/m

so I get $$v_{}1$$ and ]$$v_{}2$$ (since they are stuck together) to be 4v, but it says I'm off by a multiplative factor. Any ideas?

 

[Doc Al]

You solved for the wrong velocity. Solve for $v_f$, not $v_1$. $v_1$ is given as "v".

 

[cse63146]

yep, it's (1/4)*v, thanks.