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

The Attempt at a Solution

m_{}1v_{}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.