Finding forces acting on spring/pulley system

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The discussion focuses on analyzing a spring-pulley system to determine the relationship between spring extension and the weight of a hanging block. Key principles include the equilibrium condition where the sum of forces acting on the system must equal zero. It is clarified that the forces between the rope and the block are not third law pairs, but rather the forces between the spring and the block are. Participants are encouraged to consider the pulley axle as a separate system to derive the necessary equations. Understanding these force relationships is crucial for solving the problem effectively.
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Homework Statement



There is a spring attached to a hanging block by a rope over a pulley, with a stop on the other end. Using basic physics principles, determine the relationship between spring extension and weight of the block.

Homework Equations


F=-kd
w=mg

The Attempt at a Solution


I know that if the system is in equilibrium, the sum of forces acting on the block/spring should be zero. Also, since the force of the rope on the block and the force of the rope on the spring are third law pairs, they should be equal in magnitude but in opposite directions. Not quite sure where to go from here though.
 
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uglies1992 said:

Homework Statement



There is a spring attached to a hanging block by a rope over a pulley, with a stop on the other end. Using basic physics principles, determine the relationship between spring extension and weight of the block.

Homework Equations


F=-kd
w=mg

The Attempt at a Solution


I know that if the system is in equilibrium, the sum of forces acting on the block/spring should be zero. Also, since the force of the rope on the block and the force of the rope on the spring are third law pairs, they should be equal in magnitude but in opposite directions. Not quite sure where to go from here though.

Not like this.

Hint: First consider the axle of the pulley as the system and not the whole pulley. Consider equilibrium of spring and axle of pulley. What equation can you make for this ?
 
uglies1992 said:

Homework Statement



There is a spring attached to a hanging block by a rope over a pulley, with a stop on the other end. Using basic physics principles, determine the relationship between spring extension and weight of the block.

Homework Equations


F=-kd
w=mg

The Attempt at a Solution


I know that if the system is in equilibrium, the sum of forces acting on the block/spring should be zero. Also, since the force of the rope on the block and the force of the rope on the spring are third law pairs, they should be equal in magnitude but in opposite directions. Not quite sure where to go from here though.
Hello uglies1992 . Welcome to PF !

The force of the rope on the block and the force of the rope on the spring are not a third law pair .

The force of the rope on the block and the force of the block on the rope is a third law pair .

Similarly, the force of the spring on the block and the force of the spring on the rope is a third law pair .

There are also the force of the rope on the pulley and the force of the pulley on the rope to consider.
 
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