Questions on work done and Newton's third law

[Misr]

Hello

1- work done to push body forward is greater than to pull body backward
what is the explanation for this?can you draw the two FBD in both cases ?



2- why is nail driven in wooden wall but not in the concrete wall ؟ I guess this is somehow related to Newton's third law

Thanks

 

[jedishrfu]

This seems like homework, you should provide some reasoning before we can help.

 

[Misr]

No that's not a homework ..I thought of these questions by myself.

as for the second question I'll tell you what I can imagine about this so far>>
the hammer applies a force on the nail by pulling on it
the nail has an equal reaction in the opposite direction
the nail applies force on the wall
the wall has an equal reaction in the opposite direction
the force of the hammer on the nail is greater than the reaction of the wooden wall so the nail is driven in wood but that's not the case in concrete>>
is my explanation true?if so why the reaction of the wall is different in wood and concrete?
I hope it's a good evidence that my questions are not for homework

 

[jedishrfu]

There's another thread that discusses the hammer and nail and wood interaction:

https://www.physicsforums.com/showthread.php?t=150546

 

[sardar]

for your questions. I can provide some explanations for these phenomena:

1. The work done to push a body forward is greater than the work done to pull it backward because of the direction of the force. When pushing a body forward, the force applied is in the same direction as the displacement, resulting in positive work being done. However, when pulling a body backward, the force applied is in the opposite direction of the displacement, resulting in negative work being done. This means that more energy is required to overcome the resistance of the body and move it in the desired direction when pulling it backward compared to pushing it forward.

As for the free body diagrams (FBDs), they can help us visualize the forces acting on the body in each situation. In the case of pushing a body forward, the FBD would show a force vector pointing in the direction of the push, while in the case of pulling a body backward, the FBD would show a force vector pointing in the opposite direction of the pull.

2. The reason why a nail can be driven into a wooden wall but not into a concrete wall is indeed related to Newton's third law, which states that for every action, there is an equal and opposite reaction. When a force is applied to the nail, it exerts an equal and opposite force on the wall. In the case of a wooden wall, the force of the nail is able to overcome the resistance of the wood and penetrate it. However, in the case of a concrete wall, the resistance of the material is much greater, and the force of the nail is not strong enough to overcome it. Additionally, the composition and structure of concrete make it more difficult for the nail to create a secure hold compared to wood.

I hope this helps to answer your questions. If you have any further inquiries, please do not hesitate to ask.