Massless strings/pulleys: Finding the magnitude of the Force

[Graphire]

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...

 

[Stovebolt]

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.

 

[baba89]

I would approach this problem by first identifying the relevant equations and principles that apply. In this case, we are dealing with a system of massless strings and pulleys, which means that the tension in the string is the same on both sides of the pulley and the string has no mass. This also means that the forces acting on the pulley are balanced, so the net force on the object must be equal to zero in order for it to be lifted at a constant speed.

Using Newton's second law, we can write the equation F=ma, where F is the net force, m is the mass of the object, and a is the acceleration of the object. Since the object is being lifted at a constant speed, its acceleration is zero, and therefore the net force must also be zero.

In this case, the only forces acting on the object are its weight (mg) and the tension in the string (T). Since the net force is zero, we can set up the equation mg-T=0. Solving for T, we get T=mg. This means that the magnitude of the force F must also be equal to mg.

Therefore, the magnitude of the force F is equal to the weight of the object, which in this case is 10.3 kg multiplied by the acceleration due to gravity (9.8 m/s^2), giving us a force of approximately 101 N.