Tension and Pulleys theory question

In summary, the tension in each line of a pulley system is equal when the pulleys are massless and frictionless. This is due to the rule of thumb for block and tackle, where the mechanical advantage is equal to the number of ropes supporting the bottom pulley. By making a free body diagram of the weight and sheave, it can be determined that the tension in each line is equal.
  • #1
DanielleG
17
0

Homework Statement



  1. 17. Give the correct tension, T, in the marked rope for each situation. The rope is held so the system is stationary. All ropes and pulleys are massless and frictionless.

    A) T = W B) T = W/2 C) T = W/3 D) T = 2W E) T = 3W/2
    F) T = 2W/3 G) T = W/7 H) T = W/5 I) T = 2W/7 J) T = 2W/5

    1)
    pulley01.1.gif
    2)
    pulley01.14.gif

    3)
    pulley01.9.gif
    4)
    pulley01.10.gif

Homework Equations



No equations, mostly just theory.

The Attempt at a Solution



I've been trying to look at the various forces on each pulley compared to the next to solve this problem, as well as draw free body diagrams, but I don't feel like I'm getting anywhere, and I'm unsure of how the force will transfer from one pulley to the next, as all of the pulleys are connected. Any guidance on how to better understand the way the force changes from one pulley to the next? Thanks in advance.
 
Physics news on Phys.org
  • #2
DanielleG said:

Homework Statement



  1. 17. Give the correct tension, T, in the marked rope for each situation. The rope is held so the system is stationary. All ropes and pulleys are massless and frictionless.

    A) T = W B) T = W/2 C) T = W/3 D) T = 2W E) T = 3W/2
    F) T = 2W/3 G) T = W/7 H) T = W/5 I) T = 2W/7 J) T = 2W/5

    1)
    pulley01.1.gif
    2)
    pulley01.14.gif

    3)
    pulley01.9.gif
    4)
    pulley01.10.gif

Homework Equations



No equations, mostly just theory.

The Attempt at a Solution



I've been trying to look at the various forces on each pulley compared to the next to solve this problem, as well as draw free body diagrams, but I don't feel like I'm getting anywhere, and I'm unsure of how the force will transfer from one pulley to the next, as all of the pulleys are connected. Any guidance on how to better understand the way the force changes from one pulley to the next? Thanks in advance.
Since each pulley is massless and frictionless, then the tension in one line must be equal to the tension in the other line.

Take 1) above. If you make a FBD of the weight W and the sheave to which it is attached, what must the tension be in the two lines supporting that sheave?
 
  • #3
If you are not familiar with the simple machine called "block and tackle", I would suggest a Google search on the term.
The rule of thumb for this device is that the mechanical advantage is equal to the number of ropes (or chains) supporting
the bottom pulley. This should help you getting starting thinking on this type of problem.
The following Web Site shows some interesting examples: http://www.lhup.edu/~dsimanek/TTT-fool/fool.htm

fool-mec2.jpg
fool01c.gif

Fig. 2. Classic fool's tackle.
 
  • Like
Likes Saom Al Akib

Similar threads

Replies
12
Views
683
Replies
3
Views
2K
Replies
10
Views
4K
Replies
18
Views
692
Replies
10
Views
2K
Back
Top