Inelastic collisions between two blocks

[lilblevs11]

Homework Statement

A 2.0 kg block slides along a frictionless surface at 1.0 m/s. A second block, sliding at a faster 4.0 m/s, collides with the first from behind and sticks to it. The final velocity of the combined blocks is 2.0 m/s. What is the mass of the second block?

Homework Equations

law of conservation of momentum...

m1u1 + m2u2 = m1v1 + m2v2

The Attempt at a Solution

(2 kg * 1 m/s ) + (m2 * 4 m/s) = (2kg + m2) 2.0 m/s

2 J + (4 m/s m2) = 4 J + (2.0 m/s m2)

4 m/s m2 = 2 J + (2.0 m/s m2)

now I'm lost...

 

[netgypsy]

Just finish your algebra

by the way kgm/sec is not joule, it's just kg m/sec, which is the same as N sec

so you have the equivalent of

4m = 2 + 2m

subtracting 2m from both sides
2m = 2

m = 1kg

 

[lilblevs11]

Thanks netgypsy... now i feel like a true student. haha

 

[netgypsy]

Good job!