Recent content by rado5

Hi tiny-tim! Thank you very much for your kind help. I think my book solved the first example in a bad way! I was very naive about \vec{L}, because I wrote \vec{L} = mlr \omega \vec{e_{r}} which is wrong! Because \vec{r} = lsin \alpha \vec{e_{r}} - lcos \alpha \vec{k} and \vec{v} =...

Hi tiny-tim! There are two problems in my book. The first one is an example with its solution. As I told you before the solution is \vec{\tau}=mglsin\alpha \vec{e_{\theta}} for the problem \vec{\tau}= \vec{r} \times \vec{F} . The second one is a problem with no solution which asks "Is...

Hi tiny-tim! Thank you very much for your kind help. Yes, this is a mass m on a string of length l and tension T rotating at angle α with angular velocity ω.

Homework Statement Homework Equations The Attempt at a Solution

Dear Quinzio, Thank you very much for your help.

Thank you very much for the notification about "positive". But would you please tell me what your idea is about the ranges? especially about the ranges of "r". Are you sure that my ranges are correct?

Dear Susanne217, Thank you very much for your reply, but i have already added dA = r dr d\theta to get the result. If you calculate it you will see that I had already added it! But my problem is the ranges. I suspect about the ranges.

yes. I solved it with double integral and I got 2+pi/4.

Homework Statement Homework Equations The Attempt at a Solution Please tell me if I am wrong. I suspect about the ranges. Are my range corrrect?

Dear HallsofIvy, Thank you very much for your help. Yes my solution was wrong. At the end of my book the answer is \frac{59 \pi a^{5}}{480} and when I solved it with your method I got the correct answer. I was actually wrong about the ranges! Dear Quinzio, I used HallsofIvy's method...

Homework Statement Homework Equations The Attempt at a Solution

Dear Greg Bernhardt, My name is Reza and I live in iran! I'm atheist and I am not a brain washed man at all. I do love the US and I do respect the Americans and all the good people. We have no credit cards, paypal, western union, ... in iran. I had wanted to donate $ 30 USD to the MIT OCW...

Dear vela, thank you very much for your great generosity! Dear PhysicsForums thank you very much for your fabulous website!