Perpendicular Inelastic Collision

[sheepcountme]

Homework Statement

Two clay balls of the same mass stick together in an completely inelastic collision. Before the collision, one travels at 5.6 m/s and the other at 7.8 m/s, and their paths of motion are perpendicular. If the mass of each ball is 0.24 kg, what is the magnitude of the momentum of the combined balls after the collision?

Homework Equations

Vf=(m1v1+m2v2)/(m1+m2)

The Attempt at a Solution

I plugged everything in and for Vf I got 6.7, which was incorrect. Could someone tell me where I went wrong...

 

[rl.bhat]

Before collision two clay balls are moving in the perpendicular direction. So the resultant of two momenta is P = (P1^2 + P2^2)^1/2.
Therefore the momentum after collision is P. Total mass M is (m1 + m2). Now find Vf.

 

[sheepcountme]

Thank you!