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Physics Help

X

Xylitol

Diamond Member
I have a question about it
There are newtons 3rd law force pairs
So how do you solve for them if its a dynamics problem

For example I have 2 block next to each other and a hand is pushing on A which pushes on B

I have this given info
Force of Hand = 21 N
Mass of block A = 1 kg
Mass of block B = 2kg
Mu = .20

I dont need the answer I just need some help
on how I get the forcepairs (Fba, Fab)
 
Originally posted by: Xylitol
Ah Iunno
Im not takin AP or anyting
Just physics honors
Click to expand...

Ah...thought you were in college, anyways that stuff is easy and nice. Wait till you get to currents, and all the crap you can't visualize. Then it starts to suck (then again you might not have to take it). Good luck and get some sleep heh HS is about nothing.

 
mew LOL!

I've never seen someone spell it out like that before... mew 😀

Most people would just say u.

🙂

edit: or perhaps mu.
 
Originally posted by: silverpig
mew LOL!

I've never seen someone spell it out like that before... mew 😀

Most people would just say u.

🙂

edit: or perhaps mu.
Click to expand...

Ya at first I was like wtf then I got it.
 
Is there a question in your post?

Newton's third law states all forces are equal but opposite. The hand pushes on box A which pushes back on the hand with equal force. The same is true of A and B. B pushes on the floor with the same force. If this system is moving, the floor can only push back to a point, which is the force of friction, so the overall force is the force exerted in the forward direction is the resolution of the force of the hand minus the force of friction, and all of the intermediary forces are equal to that difference according to the 3rd law.

Sorry if that's unlcear, it's early.
 
Isn't the Fab = Fba? Equal and opposite reaction.

The free body diagram should look like

hand...............block A..........block B
--->.........<----A-----><-----B

 
Originally posted by: Atomicus
Isn't the Fab = Fba? Equal and opposite reaction.

The free body diagram should look like

hand...............block A..........block B
--->.........<----A-----><-----B
Click to expand...


Just remember OP that there will be a net force to the right as the force of the hand is greater than the force of static friction. This will cause a constant acceleration.
 
The third law is always the hardest to understand. If I punch you in the face, my fist exerts a force on your face equal to the force your face exerts on my fist. People get confused by forces and motion. Describing the collision and resultant motion is a whole different physics problem. But while they are in contact, the forces have to be equal. Otherwise they couldn't be exterting a force on each other. When you walk, the earth pushes back with the force you exert on it, so you go forward. What happens due to those forces is a change of momentum, you move, and so does the earth, but the earth moves far less.
 
It's all about the block diagram ro whatever it is called. Once you understand how to mak ethose, all the problems becomes so much easier.
 
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