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.

Question

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

Answer 1

Use conservation of linear momentum.
M1*V1 + M2*V2 = (M1+M2)*V3

The only unknown is M2 in this case, so you can solve for it.

1.9*1.8 + M2*4.5 = (1.9 + M2)*3.5
3.42 + M2 = 6.65
M2 = ____ kg

Answer 2

3.23