Two Pulleys, two weights and a string

[Petersilie23]

Homework Statement

There are two rolls and two weights. I need to define how much the right weight needs to weigh, so that both weights are in balance. The right weight is a little bit lower, but i don´t know if that has any impact. The right roll has double the radius of the left roll. Thanks for your answers! Greetings from Germany!

Relevant Equations

No

 

[berkeman]

Welcome to PF.

What do you think so far? Are you familiar with drawing a Free Body Diagram (FBD) for each weight?

 

[Petersilie23]

No never heard of it. I am thinking between 25kg and 50kg, but have no idea how you can find a fast answer in a test for example. Do you have an idea, because i´ll soon have my Physics exam.

 

[haruspex]

No never heard of it. I am thinking between 25kg and 50kg, but have no idea how you can find a fast answer in a test for example. Do you have an idea, because i´ll soon have my Physics exam.

A free body diagram considers one rigid component of the system. It illustrates all the forces that act directly on it.
Usually you need a FBD for each of several components. For two components that act on each other, each FBD will show that force, but acting oppositely.
The next step is to turn the diagrams into equations by considering the net forces in two directions (3 for a 3D problem), the torques they exert, and any resulting accelerations.

In the present case you have four components. For the pulleys, you do not care about the forces at their centres - they are just whatever they need to be to keep the pulleys in place - but you do care about the torques.

 

[Petersilie23]

Thanks for your answers: i’ll try ist. But Two questions: What impact has the double radius of the right roll: Does the right weight need to be heavier or more light. Another question: is it important that the right weight is further down than the left one and what impact does it have: Needs the weight to be more heavy or more light?

 

[phinds]

Thanks for your answers: i’ll try ist. But Two questions: What impact has the double radius of the right roll: Does the right weight need to be heavier or more light. Another question: is it important that the right weight is further down than the left one and what impact does it have: Needs the weight to be more heavy or more light?

You continue to ask questions without showing any effort on your part. That's not how this forum works. We love helping people figure out how to do things but we expect some effort to be made. We do not spoon feed answers. You have been told to do a FBD. Learn how to do that and do it. That's always the first step in solving these kinds of problems.

 

[haruspex]

But Two questions: What impact has the double radius of the right roll: Does the right weight need to be heavier or more light. Another question: is it important that the right weight is further down than the left one and what impact does it have: Needs the weight to be more heavy or more light?

Drawing the FBDs and solving the equations is how you answer those questions.