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Friction and blocks, pulling force resolving

http://img824.imageshack.us/img824/5831/friction.jpg [Broken]

The coefficient of friction between surfaces and masses are shown in figure. Here the block M3 is pulled by the force F and for a particular F friction between m2 is twice as that of m1. So what is F? I'm keep getting half the value of correct answer(provided in book), so I won't bias you with the values.
Here g is taken as 10 m/s^2
 
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Simon Bridge

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We do need to see what you tried though.
The most likely mistake is how you set up your free body diagrams.
 
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We do need to see what you tried though.
The most likely mistake is how you set up your free body diagrams.
So, can I get an answer?
 

Simon Bridge

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You certainly can.

You don't seem to be getting much joy out of these forums.
Have you read the rules and the help/tutorial-pages on how to get the most out of this place?
The thing to remember here is that we are not an answer mill ... that would be cheating.
It is your homework, you have to do the work - that is how you learn.
 
I think I gave the wrong impression here. This is not a homework, I'm a graduate student as a matter of fact. This was a problem I saw while searching for an equation in an old text book of mine. I just worked out the problem at my office and got an answer which turns out to be half the provided answer. I made a mistake which they have specially noted separately to be aware of in a small column and i re-did it and got the answer. But that special case they mentioned is quite an uncommon assumption; so I'm not sure of the textbook answer either and that's why I posted it here.
 

Simon Bridge

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You posted in the homework forums so...

So it seems your problem is not that you cannot do it then. The first step to solving a problem is to identify it.
Since you are a grad student, you should understand the approach.

What is it about the text book problem that gave you pause?
I am sure you have fellow grad students who you can show to see if they get the same answer you did - but that doesn't really help does it? As a grad student you are training to solve problems that nobody knows the answer to... you really need some way to be able to tell when you are right.

Without knowing how you handled the problem, I cannot see how you think, so cannot give a good answer.
 
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