(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A small block m=4kg and a large block m=12kg have a head on collision on a frictionless table. Before the collision, the small block is traveling 8m/s to the right and the large block is traveling 4m/s to the left.

A. If the small block bounces back at 3m/s to the left, find the final velocity of the large block.

B. Suppose instead the two blocks stick together after they collide. How many Joules of energy would be lost?

2. Relevant equations

[tex]p=mv[/tex]

[tex]KE=\frac{1}{2}mv^{2}[/tex]

3. The attempt at a solution

I will define to the right to be the positive x direction.

First I will calculate initial momentum for both blocks.

[tex]p_{i a}=mv[/tex]

[tex]p_{i a}=(4kg)(8m/s)[/tex]

[tex]p_{i a}=32kg m/s[/tex]

[tex]p_{i b}=mv[/tex]

[tex]p_{i b}=(12kg)(-4m/s)[/tex]

[tex]p_{i b}=-48kg m/s[/tex]

[tex]p_{i}=-16kg m/s[/tex]

Now final momentum:

[tex]p_{f a}=mv[/tex]

[tex]p_{f a}=(4kg)(-3m/s)[/tex]

[tex]p_{f a}=-12kg m/s[/tex]

[tex]p_{f b}=mv[/tex]

[tex]p_{f b}=(12kg)v[/tex]

[tex]p_{f b}=12v[/tex]

[tex]p_{f}=-12kg m/s + 12v[/tex]

If momentum is conserved, then

[tex]p_{i}=p_{f}[/tex]

[tex]-16kg m/s=-12kg m/s + 12v[/tex]

[tex]v=\frac{-1}{3}[/tex]

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# Homework Help: Simple momentum problem

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