Question

Please help!! I know how to work the problem to find velocities, but this one has me stumped!

A 2.0kg block slides along a frictionless surface at 1.0m/s . A second block, sliding at a faster 4.4m/s , collides with the first from behind and sticks to it. The final velocity of the combined blocks is 1.5m/s. What was the mass of the second block?

Answer 1

same old conservation of momentum

at first
p = 2 *1 + m * 4.4

at the end
p = (2+m) * 1.5

so
(2+m)(1.5) = 2 + 4.4 m

3 + 1.5 m = 2 + 4.4 m
etc