# Physics Help

posted by
**falcon306**
.

1.9 kg block slides along a frictionless surface at 1.8 m/s. A second block, sliding at a faster 4.5 m/s, collides with the first from behind and sticks to it. The final velocity of the combined blocks is 3.5 m/s.

What was the mass of the second block?

How do you set this equation up? I tried a couple of different ways and nothing worked, I only have one attempt left before I get the question wrong. Please help