Understanding the 3rd Law of Motion: Solving a Common Homework Problem

[harp AP 2010]

Homework Statement

If I pull forward on a rope tied to a box, and the box pulls back equally, how do we move at all?

Homework Equations

I think I'm over thinking this, but if my actions have equal and opposite reactions how does anything happen?

The Attempt at a Solution

 

[musiliu]

well, you move because of your mass, since it is greater than the box the box moves..

3rd law says F12 = -F21

and F= ma

so you see that the more mass you have the more force you exert, overwhelming the opposite force of the box

edit: hmm..i think I'm wrong i think it's because of the acceleration, since a = F / m , the more mass you have the less you accelerate, so the box accelerates more and it moves..but I'm not an expert on this..

 

[pongo38]

You manage to move the box by digging in your feet with more resistance than the box can muster from its friction with the ground. Imagine doing this on a frictionless surface (ice rink, say). You would just close the distance between you and the box unless you turn your skates round to obtain purchase on the ice.