# Homework Help: Physics homework -- balancing a see-saw

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1. Nov 13, 2014

### Julia Darko

How many stones (mass=2kg) are needed to lift a TV (mass=12kg) on a seesaw? What is the weight of the stones? TV? Net force?

I DEEPLY apologize if I posted this question in the wrong section AND if this question seems idiotic and simple. I am a student in high school and I am not experienced with physics, so any help/assistance/guidance will be truly appreciate.

Last edited: Nov 13, 2014
2. Nov 13, 2014

### Staff: Mentor

Welcome to the PF, Julia.

I have moved your thread to the correct section of the PF. If you review the PF Rules/Guidelines at the Info link at the top of the page, that explains where and how to post schoolwork-type questions.

Now, on your question, you will need to sum the moments (torques) around the fulcrum of the see-saw to figure out when the moment from the stones at one end balances the moment from the TV at the other end. Have you seen the equations for torque or moments so far in your classes? Is there a figure that goes with this question?

3. Nov 13, 2014

### Julia Darko

This is all that was given to me along with those questions.

4. Nov 13, 2014

### Staff: Mentor

And what have you learned about balancing moments? What are the relevant equations? Are the TV and stones the same distance from the fulcrum? Why would that matter?

5. Nov 13, 2014

### Julia Darko

I don't think distance is relevant in this particular question. I know that the weight of the stone is going to be 20 N (conceptual physics) and as for the TV, 120 N. But I don't know how MANY rocks I'm going to need to lift the TV up, nor the net force.

6. Nov 13, 2014

### Staff: Mentor

Yes, the distance of each weight from the fulcrum is very important. You still haven't posted the relevant equations for torque or moments...

7. Nov 13, 2014

### Julia Darko

... I was not given a specific equation, but the equations surrounding the lesson are f=ma, Ffriction=(μK)(Fnormal). Don't know if that's of any relevancy.

8. Nov 13, 2014

### Staff: Mentor

Those are involved, but not primarily. Please use wikipedia to look up the equations involved with torque and moments. That will give you what you need to solve this problem. Did your teacher seriously not show you those equations and gave you this homework problem? I'm not ragging on you, I'm just not understanding how your class is working.

9. Nov 13, 2014

### Julia Darko

Well, okay then. Sorry for wasting your time, but thank you anyway.