Min force to lever to lift weight

Click For Summary

Homework Help Overview

The discussion revolves around calculating the minimum force required to lift a weight using a lever and pulley system. Participants explore the concept of torque and couples in the context of mechanics.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to calculate the torque created by a weight and questions their method of using the couple about the disc. Other participants inquire about the specifics of the forces involved and the mechanics of the system, including the role of the spindle and the implications of not securing the mower while pulling the starter rope.

Discussion Status

The discussion is ongoing, with participants raising questions about the assumptions made in the calculations and the physical setup of the problem. There is a focus on clarifying the elements of the couple and the forces at play, but no consensus has been reached regarding the original poster's calculations or the mechanics involved.

Contextual Notes

Participants are working within the constraints of a homework problem, which may limit the information available for discussion. There is uncertainty about the application of concepts such as couples and the specific forces acting on the system.

toforfiltum
Messages
341
Reaction score
4

Homework Statement


upload_2015-8-31_22-49-3.png


Homework Equations


Concept of couple?

The Attempt at a Solution


First, I calculated the couple about disc, though I'm not sure if I can use this approach. Since 900 N is pulling the string of pulley downwards, I take the couple about disc as 900 x 0.4, which gives me 360 Nm. To balance this couple, the couple by F must be equal to 360. So 1.2 x F = 360 which gives me 300 N as the answer. But I'm wrong, since the answer is B. Where did I go wrong?
 
Physics news on Phys.org
toforfiltum said:
Where did I go wrong?

toforfiltum said:
900 x 0.4,
Any particular reason for using diameter?
 
Bystander said:
Any particular reason for using diameter?
I thought the 900 N exerts a couple on the disc, though I'm not sure. I'm just guessing.
 
What are/would be the two elements of the couple?
 
Bystander said:
What are/would be the two elements of the couple?
Two forces acting in opposite directions separated by a perpendicular distance.
 
What specific forces? And what distance?
 
Bystander said:
What specific forces? And what distance?
In this case there's only one force which is 900 N rotating the disc in anticlockwise direction.
 
What's holding the disc?
 
Bystander said:
What's holding the disc?
The lever turning in opposite direction?
 
  • #10
What's the "spindle" doing?
 
  • #11
Bystander said:
What's the "spindle" doing?[/
Transferring the energy?
 
  • #12
No sideways forces on it?
 
  • #13
Bystander said:
No sideways forces on it?
I totally don't know. From the picture, as the spindle rotates, it turns discs in opposite direction to the wight of 900 N on disc.
 
  • #14
What happens when you pull the starter rope on a lawnmower without putting your foot on the mower to hold it in place?
 
  • #15
Bystander said:
What happens when you pull the starter rope on a lawnmower without putting your foot on the mower to hold it in place?
The lawnmower will jump?
 
  • #16
toforfiltum said:
jump?
Any particular direction?
 
  • #17
Bystander said:
Any particular direction?
I've never used a lawnmower before:-p so I'm not too sure.It will jump away from the person pulling it?
 

Similar threads

  • · Replies 17 ·
Replies
17
Views
2K
  • · Replies 11 ·
Replies
11
Views
3K
Replies
3
Views
1K
  • · Replies 1 ·
Replies
1
Views
4K
  • · Replies 11 ·
Replies
11
Views
6K
  • · Replies 12 ·
Replies
12
Views
1K
  • · Replies 18 ·
Replies
18
Views
3K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 18 ·
Replies
18
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K