Can someone please explain this problem to me

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In summary, the conversation discusses problem 4/67 from a homework assignment and a question about the free body diagram in the solution manual. The answer is explained as the need to take apart the pliers in order to solve for internal forces. It is also mentioned that Newton's third law applies and the force of the pliers on the circle acts to squeeze it.
  • #1
doubled
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Homework Statement


https://docs.google.com/a/rams.colo...&sig=AHIEtbQGcbZbLABawi6f0FTNFXdQt_G2CA&pli=1


That's the link to the problem. It's problem 4/67. I don't understand why in the FBD in my solution manual they took away the 30lb force pointing up and have the force on the circle thing pointing in the +x and -y direction. Can someone explain this to me please? Thanks.
 
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  • #2
doubled said:

Homework Statement


https://docs.google.com/a/rams.colo...&sig=AHIEtbQGcbZbLABawi6f0FTNFXdQt_G2CA&pli=1


That's the link to the problem. It's problem 4/67. I don't understand why in the FBD in my solution manual they took away the 30lb force pointing up and have the force on the circle thing pointing in the +x and -y direction. Can someone explain this to me please? Thanks.
since the force on the pin is internal, you have to 'take apart' the pliers in a 'free body diagram' of one of the 2 pieces, in order to solve for the internal forces. When you do this, the other 30 lb force is not in the picture. The force of the circle thing on that part of the pliers is perpendicular (normal) to the contact point, and can be broken into its horizontal and vertical components.
 
  • #3
Oh thanks a lot. So if we look at the top part wouldn't the 30lb force pointing down be applying a force on the circle that should be pointed in the -x and +y direction not the opposite? Like if I had a pair of pliers and I only press down on the upper that would make the mouth push up.
 
  • #4
doubled said:
Oh thanks a lot. So if we look at the top part wouldn't the 30lb force pointing down be applying a force on the circle that should be pointed in the -x and +y direction not the opposite?
Well yes, that's Newton's third law, the force of the pliers on the circle act to squeeze it . But when you draw the FBD of the pliers, the force of the circle thingy acting on the pliers points in the +x and -y direction (down and to the right), which you can show by summing moments about the pin.
if I had a pair of pliers and I only press down on the upper that would make the mouth push up.
Well, you can't just press down on the upper part, you have to sqeeze the handles together with an equal but opposite force on each in order to make the thing work. The lower jaw moves up, and the upper jaw moves down, as if it were biting the 'circle' (a nut or bolt or rod, etc).:eek:
 
  • #5


Sure, I'd be happy to explain this problem to you. First, let's break down the problem statement. The problem is asking you to compute the force supported by the pin at point A for a pair of slip-joint pliers. This means that you need to determine the magnitude and direction of the force acting on the pin at point A in order for the pliers to function properly.

Now, let's take a look at the provided link. This is a solution manual for a specific problem (4/67) in a mechanics course. The problem involves a pair of slip-joint pliers with a 30lb force acting on it in the upward direction. The solution manual shows a free body diagram (FBD) for the pliers, which is a diagram that shows all the forces acting on an object. In this case, the FBD shows the 30lb force and the force acting on the pin at point A.

The confusion here seems to be with the direction of the force on the pin at point A. In the solution manual, the force is shown pointing in the +x and -y direction. This is because the force on the pin is a combination of two forces - one in the x-direction and one in the y-direction. These two forces are necessary to keep the pliers in equilibrium, meaning they are not moving or rotating. The force in the x-direction is needed to counteract the 30lb force acting upward, while the force in the y-direction is needed to keep the pliers from rotating.

I hope this helps to clarify the problem for you. If you have any further questions, please let me know.
 

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When someone asks for an explanation of a problem, they are seeking clarification or understanding about a specific issue or concept. They may be struggling to comprehend the problem or need more information to fully understand it.

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Clear explanations help others understand the problem and its potential solutions. This can lead to more effective problem-solving and prevent mistakes or misunderstandings. Additionally, clear explanations can help foster a better learning environment and promote mutual understanding.

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