Engineering Questions on Forces & Friction: Analyzing Plate & Block Motion

AI Thread Summary
The discussion centers on the dynamics of a plate and block system, focusing on the forces acting on them. The first question addresses the presence of horizontal acceleration (Ax) despite no horizontal forces, suggesting that the pin provides necessary centripetal force for the plate's motion. The second question involves confusion about the block's movement under friction, with clarification that if the surface accelerates, friction can either move the block with it or cause it to slip. The centripetal force, derived from the pin, is essential for the plate's rotation, while the block's center of mass is influenced by gravity and the pin's reaction force. Overall, the interactions between these forces dictate the system's behavior in motion.
Pipsqueakalchemist
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Homework Statement
Questions below
Relevant Equations
Newton’s 2nd law
So I have questions on two separate questions. The first question is about the fbd of the plate attached to the pin. How can there be an Ax since there’s no other force in the horizontal direction wouldn’t the plate start moving on the x-direction due to imbalanced forces.

Second question about the elevator question. I knew how to do the problem but I do have some confusion. I have my work below and for the 0.4Nb=100*1.5*alpha part, I’m confused bc since friction is the only force horizontal force acting on the block wouldn’t the block move and slip?
 

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Without the pin restricting movement along the x-axis, the center of mass of the block will move vertically down.
The pin provides the centripetal acceleration that deviates the mass from the more natural straight vertical trajectory.
 
But when you write Equation of motion in the x direction. Ax is the only force so wouldn’t that imply it’s accelerating in the x direction. I originally thought the FBD would just be W and Ay
 
Pipsqueakalchemist said:
But when you write Equation of motion in the x direction. Ax is the only force so wouldn’t that imply it’s accelerating in the x direction. I originally thought the FBD would just be W and Ay
The diagram shows the CoM of the plate moving in a circle in the x-y plane and not initially in the y-direction. There must, therefore, be a force on the plate (from the hinge) in the x-direction.
 
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Pipsqueakalchemist said:
Second question about the elevator question. I knew how to do the problem but I do have some confusion. I have my work below and for the 0.4Nb=100*1.5*alpha part, I’m confused bc since friction is the only force horizontal force acting on the block wouldn’t the block move and slip?
I'm not sure where the confusion lies. If a block is resting on a surface and the surfaces accelerates in the horizontal direction, then the friction may accelerate the block with the surface; or, if the friction is insufficient, the block will slide backwards relative to the surface.
 
PeroK said:
The diagram shows the CoM of the plate moving in a circle in the x-y plane and not initially in the y-direction. There must, therefore, be a force on the plate (from the hinge) in the x-direction.
Oh so the Ax acts as the centripetal force right?
 
Pipsqueakalchemist said:
Oh so the Ax acts as the centripetal force right?
The centripetal force has an x-component, yes.
 
PeroK said:
The centripetal force has an x-component, yes.
So the pin A is the centripetal force causing the plate to rotate around A
 
Lnewqban said:
Without the pin restricting movement along the x-axis, the center of mass of the block will move vertically down.
The pin provides the centripetal acceleration that deviates the mass from the more natural straight vertical trajectory.
Wait how do you it would move down. Why couldn’t it move up or stay in static equilibrium?
 
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Pipsqueakalchemist said:
So the pin A is the centripetal force causing the plate to rotate around A
The centripetal force is a component of the net force: the vector addition of gravity and the reaction force at the pin.
 
  • #11
Pipsqueakalchemist said:
Wait how do you it would move down. Why couldn’t it move up or stay in static equilibrium?
Because the direction of the represented force (24 Kg x 9.8 m/s^2).
 
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