Newtons Laws - Boxes connected with a cord

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Homework Help Overview

The problem involves two blocks connected by a cord over a pulley, with one block resting on a tabletop and the other hanging. The scenario includes considerations of friction and acceleration as the blocks are released from rest.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculation of friction force and the gravitational force acting on the hanging block. Questions arise regarding the relationship between tension in the rope and the weight of the hanging block, as well as the application of Newton's second law to find acceleration and velocity.

Discussion Status

Some participants have provided insights into the tension in the rope and the need to set up equations for both blocks to solve for tension and acceleration. There is an acknowledgment of the need for further exploration of these equations, but no consensus has been reached on a specific approach.

Contextual Notes

The original poster has attempted calculations but encountered difficulties in determining the velocity of the blocks. There is a mention of the coefficient of kinetic friction and the specific masses of the blocks involved.

hsestudent
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Homework Statement


A block A (mass 2.25k) rests on a tabletop. It is connected by a horizontal cord passomg over a light, frictionless pulley to a hanging block B (mass 1.3kg). The coeffisient of kinetic friction between block A and the tabletop is 0.45. After the block is released from the rest,
fint the speed of each block after moving 3cm.


Homework Equations





The Attempt at a Solution


I found the frictionforce by:

Frictionforce = coeffisient * N (where N = G of block A).

Frictionforce = 9,93 N.

The force on the rope will be = the G (gravityforce) on block B.

ForceOnRope = 12,75N

Then I tried to use Newtons second law to find the acceleration, but this attempt failed when I tried to find the velocity of the boxes, which will be the same?
 
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hsestudent said:
The force on the rope will be = the G (gravityforce) on block B.

ForceOnRope = 12,75N
The tension in the rope does not equal the weight of block B. If it did, then the blocks would be in equilibrium.

Call the tension T. Set up equations for both blocks and you'll be able to solve for the tension and the acceleration.
 
tension

Note that the Tension will be the same throughout the rope. So if you set up the forces on each block and solve them for the Tension, you can then set those 2 equations equal to solve for other variables, such as the acceleration. Then you can use kinematics to solve for the speed.
 
Last edited:
Thanks, will try this tomorrow morning!
 

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