Balancing Weight on an 8m Pole: Find the Solution

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Discussion Overview

The discussion revolves around a physics problem involving a horizontal pole of 8 meters with a mass of 200 kg tied to it. Participants are exploring how to determine the position along the pole where the weight should be tied, given that one person supports four times the weight of the other. The scope includes mathematical reasoning and problem-solving techniques related to torque and equilibrium.

Discussion Character

  • Mathematical reasoning
  • Homework-related
  • Technical explanation

Main Points Raised

  • One participant presents the problem and requests assistance in determining where to tie the weight on the pole.
  • Another participant suggests making a sketch and outlines a method to analyze the forces and torques acting on the pole, defining the forces exerted by the man and the boy.
  • A later reply challenges the previous suggestion by stating that the force F cancels out in the torque equation, leading to a simplified equation for d, which can be solved directly.
  • This participant emphasizes the importance of expressing the final answer as a distance from a specific person and in meters.

Areas of Agreement / Disagreement

There is disagreement regarding the approach to solving the problem, particularly about whether to find the force F or to solve directly for the distance d. Participants have not reached a consensus on the best method to proceed.

Contextual Notes

The discussion does not clarify certain assumptions, such as the distribution of weight along the pole or the effects of any additional forces that may be present. The mathematical steps leading to the solution are also not fully resolved.

Shah 72
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A man and a boy hold opposite ends of 8m long pole which is horizontal. A mass of 200 kg is tied to the pole. If the man is to support four times as much weight as the boy where along the pole must the weight be tied?
Can someone please help
 
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Hint: Make a sketch.

Put the man on the left and the boy on the right. Let the mass hang a distance d from the man. Then the mass is a distance 8 - d from the boy. Call the force the boy exerts F. Then the man exerts 4F. The pole does not rotate so the net torque on it is 0 Nm. Pick an axis, say at the man and call a clockwise rotation positive. Then the net torque is
0 = d(4F) - (8 - d)F. Now pick an axis at the mass and see if you can find F.

-Dan
 
topsquark said:
Hint: Make a sketch.

Put the man on the left and the boy on the right. Let the mass hang a distance d from the man. Then the mass is a distance 8 - d from the boy. Call the force the boy exerts F. Then the man exerts 4F. The pole does not rotate so the net torque on it is 0 Nm. Pick an axis, say at the man and call a clockwise rotation positive. Then the net torque is
0 = d(4F) - (8 - d)F. Now pick an axis at the mass and see if you can find F.

-Dan
Thank you so so much!
 
You CAN'T "find F" because F cancels out of that equation.

0= d(4F)- (8- d)F. Dividing by F

0= 4d- (8- d)= 4d- 8+ d= 5d- 8

and you can easily solve for d, not F.

Don't forget that the answer must be given as a distance from a specific person and must be stated in meters.
 

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