Massless strings/pulleys: Finding the magnitude of the Force

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SUMMARY

The discussion focuses on calculating the magnitude of the force F required to lift a mass of 10.3 kg using a massless string and two massless, frictionless pulleys. The key insight is that when lifting the object at a constant speed, the net force acting on the system is zero, meaning the applied force F must equal the weight of the mass. The correct formula to use is F = m * g, where g is the acceleration due to gravity (approximately 9.81 m/s²). Thus, the magnitude of the force F is 10.3 kg * 9.81 m/s², resulting in approximately 100.8 N.

PREREQUISITES
  • Understanding of Newton's laws of motion
  • Familiarity with the concepts of force, mass, and weight
  • Basic knowledge of pulleys and their mechanical advantage
  • Ability to apply the equation F = m * g
NEXT STEPS
  • Study the principles of mechanical advantage in pulley systems
  • Learn about Newton's second law of motion and its applications
  • Explore the concept of tension in strings and ropes
  • Investigate the effects of friction in pulley systems and how to account for it
USEFUL FOR

Students studying physics, particularly those focusing on mechanics, as well as educators and anyone interested in understanding the dynamics of forces in pulley systems.

Graphire
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Homework Statement


A massless string runs around two massless, frictionless pulleys, as shown in the figure below. An object with mass m = 10.3 kg hangs from one pulley. A force F is exerted on the free end of the string. What is the magnitude of the force F if the object is lifted at a constant speed?


Homework Equations


I'm guessing around 1/2m x v^2 but I really don't have a clue...


The Attempt at a Solution


Well so far I got that the force goes in the y-axis so that he factors involving the y-axis is the weight and tension. Since the question does not give me tension and I really don't know what formula to use to figure it out I'm quite lost.

There's also a diagram but I don't know how to put it up here...
 
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Graphire said:

Homework Statement


A massless string runs around two massless, frictionless pulleys, as shown in the figure below. An object with mass m = 10.3 kg hangs from one pulley. A force F is exerted on the free end of the string. What is the magnitude of the force F if the object is lifted at a constant speed?

Homework Equations


I'm guessing around 1/2m x v^2 but I really don't have a clue...

The Attempt at a Solution


Well so far I got that the force goes in the y-axis so that he factors involving the y-axis is the weight and tension. Since the question does not give me tension and I really don't know what formula to use to figure it out I'm quite lost.

There's also a diagram but I don't know how to put it up here...

Can you try to describe the figure? Give the path of the string and position of the pulleys and mass, if you can.

Also, (1/2) m * v2 will give you units of work or energy. It sounds more like you need an equation dealing with force, mass, and acceleration.
 

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