Tension and Pulleys Cannot understand this problem

In summary, the conversation discusses a problem involving a man sitting in a bosun's chair attached to a massless rope and a frictionless pulley. The combined mass of the man and the chair is given and the question asks for the force magnitude that the man must pull on the rope in order to rise with a constant velocity. The confusion arises from the equation 2T=mg+ma, where T represents tension, m represents mass, and a represents acceleration. The person is unsure why there are two tension forces and if they can cancel each other out. A free body diagram is suggested to understand the direction of the tension forces.
  • #1
goddard
1
0
Tension and Pulleys...Cannot understand this problem

So this is NOT for homework, (I'm doing practice problems reviewing for a final), but this is a textbook question that might as well be homework.

This is the question:

Figure 5-53 shows a man sitting in a bosun’s chair that dangles from a massless rope, which runs over a massless, frictionless pulley and back down to the man’s hand. The combined mass of man and chair is 95.0 kg. With what force magnitude must the man pull on the rope if he is to rise (a) with a constant velocity?


After looking at the solution, the part that confuses me is the 2T. I don't understand why 2T=mg+ma (m is the mass of the man-pulley) is the equation that we can use. Doesn't the tension cancel out so that mg=F, where F is the force of the hand pulling?

Thank you for taking the time to read this.
 
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  • #2
goddard said:
After looking at the solution, the part that confuses me is the 2T. I don't understand why 2T=mg+ma

Draw a free body diagram. How many tension forces T are there?

goddard said:
Doesn't the tension cancel out so that mg=F, where F is the force of the hand pulling?

What direction are these tensions in? Is it possible for them to "cancel" each other out?
 

1. What is tension and how is it related to pulleys?

Tension is a force that is exerted on an object in a certain direction. In the context of pulleys, tension refers to the force that is applied to the rope or cable that is attached to the pulley. This force is used to lift or move heavy objects.

2. How does a pulley system work?

A pulley is a simple machine that consists of a grooved wheel and a rope or cable. When the rope is passed through the groove of the wheel and attached to an object, pulling on one end of the rope will cause the object to move in the opposite direction. This is due to the mechanical advantage of the pulley, which reduces the amount of force needed to lift or move heavy objects.

3. Why is it important to understand tension and pulleys?

Tension and pulleys are important concepts in physics and engineering. They are used in various applications such as construction, transportation, and mechanical systems. Understanding how tension and pulleys work allows us to design and build efficient and safe machines and structures.

4. Can tension and pulleys be used to create a mechanical advantage?

Yes, tension and pulleys can be used to create a mechanical advantage. A mechanical advantage is the ratio of the output force to the input force. In the case of pulleys, the mechanical advantage is determined by the number of ropes supporting the object. The more ropes, the greater the mechanical advantage, making it easier to lift or move heavy objects.

5. What are some real-life examples of tension and pulleys?

Tension and pulleys are commonly used in elevators, cranes, and construction equipment to lift heavy loads. They are also used in exercise machines, such as weightlifting machines, to provide resistance. Other examples include window blinds, flagpoles, and sailboats.

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