Pulling force for Bosun's chair?

  • Thread starter Theorγ
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In summary, the man must pull down on the rope with a force equal to his weight in order to maintain constant velocity while being pulled up on the other end. This is due to Newton's third law, which states that every action has an equal and opposite reaction.
  • #1
Theorγ
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Homework Statement


A pulley is attached to the ceiling, with a rope going over that pulley and both objects are mass less. At one end of the rope, a Bosun's chair with a man sitting on it is attached, and the man is holding on to the other end of the rope. The man and chair's mass combined is 95 kg. What is the force the man must use to pull himself up at constant velocity?

Homework Equations


[tex]F_{net} = m a[/tex]

The Attempt at a Solution


I first drew all the forces on the system by using the following equations:

Forces on the man and chair
[tex]-F_{g} + T = m a[/tex]

Forces on the other end of rope
[tex]F_{pull} - T = m a[/tex]

Definition of Constant velocity
[tex]a = 0[/tex]

Subbing in the given values will give the notion that the man must pull his own weight to go up, but apparently this is not the answer, so what am I missing?
 
Last edited:
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  • #2
Theorγ said:

Homework Statement


A pulley is attached to the ceiling, with a rope going over that pulley and both objects are mass less. At one end of the rope, a Bosun's chair with a man sitting on it is attached, and the man is holding on to the other end of the rope. The man and chair's mass combined is 95 kg. What is the force the man must use to pull himself up at constant velocity?

Homework Equations


[tex]F_{net} = m a[/tex]

The Attempt at a Solution


I first drew all the forces on the system by using the following equations:

Forces on the man and chair
[tex]-F_{g} + T = m a[/tex]

Forces on the other end of rope
[tex]F_{pull} - T = m a[/tex]

Definition of Constant velocity
[tex]a = 0[/tex]

Subbing in the given values will give the notion that the man must pull his own weight to go up, but apparently this is not the answer, so what am I missing?
You are missing the fact that if you draw a free body diagram of the chair with the man on it, there are two ropes pulling up on them...one on the man and one on the chair. The tension on each rope must be equal, and the sum of those 2 tensions must equal the weight of the man and chair.
 
  • #3
There's a rope pulling on the man?
 
  • #4
The man pulls down on the rope. According to Newton's third law, the rope will pull up on the man with an equal force.

If you imagine a man hanging on to a rope half way up a cliff, you will see this force must exist!
 
  • #5
Delphi51 said:
The man pulls down on the rope. According to Newton's third law, the rope will pull up on the man with an equal force.

If you imagine a man hanging on to a rope half way up a cliff, you will see this force must exist!

So do you mean:

[tex]-F_{g} + F_{n} + F_{pull} = m a[/tex]
[tex]F_{pull} - F_{n} - F_{g} = m a[/tex]
 
Last edited:
  • #6
You have already established that a = 0, so if you look at the forces on the man only, it's Ft + Fn - Fg = 0 ( the normal force acts in the same direction as the tension force). But you still cannot find Ft ,since Fn is also unknown. So instead, draw a FBD of the man-chair system, isolating them from the pulley. Then the normal force becomes internal to your system, and does not enter into the equation using Newton 1. Only the rope tensions and the weights act when looking at it this way. Solve for Ft.
 

1. What is a Bosun's chair?

A Bosun's chair is a type of suspended seat used by sailors, workers, and climbers to perform tasks at height. It typically consists of a small seat made of wood or metal, and is attached to a single rope or cable that is suspended from an overhead structure.

2. How is pulling force calculated for a Bosun's chair?

The pulling force for a Bosun's chair is calculated by taking into account the weight of the person sitting in the chair, the weight of any additional equipment or tools being used, and the angle of the rope or cable attached to the chair. The greater the weight and angle, the more pulling force will be required to safely lift the person and equipment.

3. What factors can affect the pulling force for a Bosun's chair?

The pulling force for a Bosun's chair can be affected by several factors, including the weight of the person and equipment being lifted, the angle of the rope or cable, the condition of the rope or cable, and the strength and technique of the person pulling the rope. Environmental factors such as wind or rain can also impact the pulling force required.

4. How can the pulling force for a Bosun's chair be reduced?

The pulling force for a Bosun's chair can be reduced by decreasing the weight of the person and equipment being lifted, using a lower angle for the rope or cable, and ensuring the rope or cable is in good condition. Proper body mechanics and using pulleys or other mechanical advantage systems can also help to reduce the pulling force required.

5. What safety precautions should be taken when using a Bosun's chair?

When using a Bosun's chair, it is important to ensure that the chair is properly attached to the rope or cable, and that the rope or cable is securely anchored to a strong and stable structure. The person sitting in the chair should also wear a safety harness and be properly trained on how to use the chair and associated equipment. Regular inspections and maintenance of the chair and equipment should also be conducted to ensure safety.

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