Understanding Tension in a Block and Tackle System

In summary, the conversation discusses the tension in the rope needed for the boy to raise himself at a constant rate while using a block and tackle. There is a discrepancy between the number of tensions shown in the book and the number calculated by the individual involved in the conversation. It is eventually clarified that the tension occurs five times due to the lower block and the boy being considered as one system.
  • #1
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Homework Statement



The boy is lifting himself using the block and tackle shown. If the weight of the block and tackle is negligible, and the combined weight of the boy and the beam he is sitting on is 120 lb, what force does he have to exert on the rope to raise himself at a constant rate? (Neglect the deviation of the ropes from the vertical.)

I drew a FBD for the bottom of the block with the weight going down and 4 tensions pulling up, each with a force of 30lb, but the book has 5 tensions. Which one is correct?

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  • #2
Do you dispute that the rope the boy is holding is also at tension T? Do you dispute that all five tensions act on the boy+beam system?
It might be clearer to you if you consider the lower pulley block and the boy+beam separately. What is the tension in the rope connecting them?
 
  • #3
haruspex said:
Do you dispute that the rope the boy is holding is also at tension T? Do you dispute that all five tensions act on the boy+beam system?
It might be clearer to you if you consider the lower pulley block and the boy+beam separately. What is the tension in the rope connecting them?

oh, so the tension occurs 5 times b/c 4 times at the lower block, but then also from the boy like the picture because the whole thing is one system, and the block is only part of it.

thanks for the explanation to clear it up!
 

FAQ: Understanding Tension in a Block and Tackle System

What is a block and tackle system?

A block and tackle system is a mechanical device that uses a combination of fixed and movable pulleys to provide mechanical advantage, making it easier to lift heavy objects. It is commonly used in cranes, elevators, and other lifting systems.

How does a block and tackle system work?

A block and tackle system works by distributing the weight of the load evenly between the fixed and movable pulleys. As the rope or cable is pulled, the pulleys rotate and the load is lifted. The more pulleys in the system, the greater the mechanical advantage.

What are the different types of block and tackle systems?

There are three main types of block and tackle systems: the gun tackle, the luff tackle, and the double tackle. The gun tackle uses a single fixed pulley and a single movable pulley, the luff tackle uses two fixed pulleys and one movable pulley, and the double tackle uses two fixed pulleys and two movable pulleys.

What are the advantages of using a block and tackle system?

The main advantage of using a block and tackle system is that it allows for heavy loads to be lifted with less force. This can reduce the risk of injury and make tasks easier and more efficient. Additionally, the use of pulleys can also change the direction of the force, allowing for pulling or lifting in different directions.

What are some common applications of block and tackle systems?

Block and tackle systems have a wide range of applications, including in construction, shipbuilding, and transportation. They are also commonly used in theatrical productions to lift and move heavy set pieces and props. In everyday life, block and tackle systems can be found in window blinds, flagpoles, and even some exercise equipment.

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