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## Main Question or Discussion Point

I’m confused about conservation of momentum. I remember learning that the momentum before a collision is the same as after it:

So I do that for a mass M

M

and I get an equation for the velocity

Now let’s say that M

But since M

**P**_{initial}=**P**_{final}.So I do that for a mass M

_{1}colliding with another mass M_{2}that’s initially at rest,M

_{1}x**V**_{1}_{initial}+ 0 = M_{1}x**V**_{1}_{final}+ M_{2}x**V**_{2}_{final}and I get an equation for the velocity

**V**_{2}_{final},**V**_{2}_{final}= (M_{1}/M_{2}) x (**V**_{1}_{initial}-**V**_{1}_{final}) .Now let’s say that M

_{2}is so large that in the limit it becomes infinite. In that case,**V**_{2}_{final}= 0, so that**V**_{1}_{final}=**V**_{1}_{initial}.But since M

_{1}bounces off of M_{2}, shouldn't**V**_{1}_{final}and**V**_{1}_{initial}be pointing in opposite directions?