• Support PF! Buy your school textbooks, materials and every day products Here!

Pulleys and Springs: Really stupid question

  • #1
3,003
2
So I am trying to follow along this example in the text to find keq of the system.

I can follow everything up until the point that they say: "It follows that x=2(x1+x2)

where:

x = displacement of mass
x1 =displacement of Pulley1cm
x2 =displacement of Pulley2cm

I am not seeing it. I am also very tired. So please help me and then slap me :smile:

Picture6-3.png
 

Answers and Replies

  • #2
rl.bhat
Homework Helper
4,433
5
For the time being, suppose k2 is not operating. When the pulley1 moves up through x1, what is the distance moved by the mass ?
 
  • #3
3,003
2
Yeah. I don't see it. How ca I relate anything to x?

Like rl.bhat says: If k2 was not operating, I know that 2W=k1*x1 ... but I
don't see how that helps?
 
  • #4
3,003
2
Anyone?
 
  • #5
rl.bhat
Homework Helper
4,433
5
Just compare the movement of the pulley and release of the rope at mass end.
When the pulley1 moves through x1, mass moves through y1 distance ,then y1 = 2x1. Similarly for pulley 2, y2 = 2x2. So the distance moved by the mass y1 + y2 = x = 2(x1 + x2)
 
  • #6
3,003
2
Okay. I mean, I believe you. I just don't see it.
 
  • #7
rl.bhat
Homework Helper
4,433
5
Okay. I mean, I believe you. I just don't see it.
When p1 moves up through x1, on both side of the pulley x1 rope is released. That adds up to 2x1.
 
  • #8
3,003
2
When p1 moves up through x1, on both side of the pulley x1 rope is released. That adds up to 2x1.
Ahh. I think I see it now. Thanks for your patience!
 

Related Threads for: Pulleys and Springs: Really stupid question

  • Last Post
Replies
19
Views
9K
  • Last Post
Replies
22
Views
2K
  • Last Post
Replies
8
Views
3K
  • Last Post
Replies
10
Views
18K
  • Last Post
Replies
3
Views
708
  • Last Post
Replies
1
Views
928
  • Last Post
Replies
6
Views
1K
  • Last Post
Replies
11
Views
3K
Top