Tension with a with a massless rope

Click For Summary

Homework Help Overview

The discussion revolves around a physics problem involving a massless pulley system with two boxes of different masses. The original poster presents two scenarios: one where friction holds the system in equilibrium and another where friction is negligible and the system begins to move. The focus is on determining the tensions in the ropes connecting the pulley to the boxes and the ceiling.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the relationships between the tensions T0, T1, and T2 in both scenarios. Questions arise regarding the correctness of the calculated tensions and the assumptions about equilibrium in the moving scenario.

Discussion Status

Participants are actively questioning the assumptions made about the system's equilibrium and the resulting tensions. There is a mix of interpretations regarding the relationships between the tensions, with some participants expressing doubt about the original calculations and suggesting alternative views.

Contextual Notes

The problem involves assumptions about massless ropes and pulleys, and the effects of friction on the system's behavior. The original poster's calculations are challenged, leading to further exploration of the underlying physics principles.

kbka
Messages
25
Reaction score
0
Hi...

I have a little assignment where I'm not quite sure, what would be the correct answer...

A massless pulley, is mounted to the ceiling with a massless rope. Over the pulley runs another massles rope, with a box with mass m in one end and a box with mass 2*m in the other.

Q1) In this first question, the friction holds the whole system in equilibrium.
What is the tension T0 between pulley and ceiling, T1 between pulley and box with mass m, T2 between pulley and box with mass 2*m

A1: T1=m*g, T2=2*m*g and T0=(m*2m)*g=3*m*g

Q2) Now, friction is negligible, and the system starts to move... What is the tension T0, T1 and T2
A2: I have calculated T1=T2=4/3*mg and T0=3*m*g (still)

Is the last answer for T0 correct? My assumption is that this part of the system (pulley+rope) is still in equilibrium, and therefore Fres=m*g-T=0
 
Physics news on Phys.org


kbka said:
Hi...

I have a little assignment where I'm not quite sure, what would be the correct answer...

A massless pulley, is mounted to the ceiling with a massless rope. Over the pulley runs another massles rope, with a box with mass m in one end and a box with mass 2*m in the other.

Q1) In this first question, the friction holds the whole system in equilibrium.
What is the tension T0 between pulley and ceiling, T1 between pulley and box with mass m, T2 between pulley and box with mass 2*m

A1: T1=m*g, T2=2*m*g and T0=(m*2m)*g=3*m*g

Q2) Now, friction is negligible, and the system starts to move... What is the tension T0, T1 and T2
A2: I have calculated T1=T2=4/3*mg and T0=3*m*g (still)

Is the last answer for T0 correct? My assumption is that this part of the system (pulley+rope) is still in equilibrium, and therefore Fres=m*g-T=0

If T1 + T2 = T0, then isn't T0 = 8/3mg ?
 
LowlyPion said:
If T1 + T2 = T0, then isn't T0 = 8/3mg ?

Thank you for the reply, but i highly doubt that's the case... I have drawn the situation to make it more clear...

http://peecee.dk/upload/view/136892
 
kbka said:
Thank you for the reply, but i highly doubt that's the case... I have drawn the situation to make it more clear...

http://peecee.dk/upload/view/136892

Is it your suggestion then that T1 + T2 ≠ T0 ?

Looks to me like T1 = m*(g + 1/3g) = T2 = 2m*(g - 1/3g)

2*T1 = 2*T2 = 8/3*m*g = T0
 

Similar threads

Falling mass, additionally accelerated by a rope
  • · Replies 18 ·
Replies
18
Views
2K
Newton's law problem: Helicopter lifting a box with a rope
  • · Replies 5 ·
Replies
5
Views
3K
Calculating acceleration of a prism and block connected to a wall through a rope and pulley
  • · Replies 4 ·
Replies
4
Views
1K
Monkey accelerating up and down a rope
  • · Replies 38 ·
2
Replies
38
Views
5K
Newton's Second Law (Pulley Sustem)
  • · Replies 3 ·
Replies
3
Views
2K
A rope, a pole, and some tension
  • · Replies 11 ·
Replies
11
Views
2K
System with Pulleys and a Rope That Might Break
  • · Replies 26 ·
Replies
26
Views
3K
Tension in a string which connects 3 pulleys
  • · Replies 12 ·
Replies
12
Views
2K
Pulleys with Torque: Free Body Diagram Analysis
  • · Replies 34 ·
2
Replies
34
Views
4K
Problem with pulleys - two fixed and one movable
  • · Replies 22 ·
Replies
22
Views
2K