Hey.. I don't know exactly how to get the solution for this one...

doubleudoubleudouble dot physikerboard.de/files/fahrzeug_223.jpg

(its a sketch i made with paint^^)

We assume there are no frictions at all and we only look at the masses M, m1 and m2.

I want to know how much force do i have to give to push M in such a way that it accelerates so fast that m1 and m2 wont move related to M?

2 answers

No friction? then the inertia on m1 tending to move it back (m1*a) is pulling on the cord, equalling in tension m2*g

first, what is a:

F=(M+m1+m2)a solve for a.

then m1*a=m2*g
m1(F/(M+m1+m2))=m2g

solve for F, check my math.
Ah great thank you. I got problems with it because there are no frictions...i can hardly imagine how the masses behave but ill get an "eye" for it. Seems very right, big thanks!