Newton's 3rd law and its affect

[icecomet]

Homework Statement

When a bike crashes into a metal fence why does the fence bend when the magnitude of the forces that they exert upon each other are the same?

Homework Equations

FAB = -FAB

The Attempt at a Solution

I think this is because the bike has more mass than the fence... but i am not sure how this is applied.

 

[lubuntu]

no f=ma so the mass is already accounted for, should certain materials or apparatuses be able to withstand more force than others?

 

[lubuntu]

and you also have to remember that the opposite forces work on different bodies