Marble collisions, momentum, velocity

[KatieLynn]

Homework Statement

Marble A, mass 5g moves at a speed of 20 cm/s. It collides with a second marble B, mass 10 g, moving at 10 cm/s in the same direction. After the collision, marble A continues with a speed of 8 cm/s in the same direction. A) Calculate the momentum of each marble before the collision. B) Calculate the momentum of each marble after the collision. C) What is the speed of marble B after the collision?

Homework Equations

F=m(Vf-Vi)/t

The Attempt at a Solution

I converted all the numbers first

Mass A= .005kg
Vi A = .2 m/s
Mass B= .1 m/s
Vi B = .2 m/s
V after = .8 m/s

A) Marble A:
(.005kg)(02m/s) = .001 kg*m/s

Marble B:
(.01kg)(.1m/s)=.001 kg*m/s

B) (.001+.001)=(.005kg+.01kg)V
v=1.33 m/s

What did I do wrong in B? I'm pretty sure A is right.

 

[Senjai]

Just skimming over,

Total Momentum After = Total Momentum Before

P2' = P2

m2v2' = m2v2
(.01 Kg)(.08 m/s) = (.01 Kg)v2

algebra to isolate v2do you see what i did? Momentum after must equal momentum before, you know the momentum before the collision was m2v2, it has to equal momentum after, which is m2v2' your only unknown is v2' which you can solve using your data.. i did this usuing your definitions for the mass and velocities, i didn't check those.