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-   -   How does one do this question? (http://www.physicsforums.com/showthread.php?t=653612)

EPFLstudent Nov20-12 09:51 AM

How does one do this question?
 
Figure attached below. You have a big block of mass M and a small block of mass m. When m=3kg, the acceleration of the large block is 0.6ms-2. When m=4kg, the acceleration of the large block is 1.6ms-2. The dynamic friction coefficient between the large block and the surface it slides on is μ. There is no friction between any other surface. Questions:

a) Express the relationship between the movement of block m and block M
b) Derive expressions for the motion of block m and block M.
c) Determine the mass of block M and the dynamic friction coefficient, μ, between it and the surface it slides on.

http://i.imgur.com/FDmZ7.jpg

jbriggs444 Nov20-12 10:02 AM

Re: How does one do this question?
 
Nice problem. So what have you got so far? How does the motion of mass m relate to the motion of mass M?

EPFLstudent Nov20-12 10:19 AM

Re: How does one do this question?
 
I know that [itex] x_m = 2 x_M [/itex], so that the small block moves two times as much as the big block. My problem is decomposing the forces.

SteamKing Nov20-12 10:32 AM

Re: How does one do this question?
 
Draw free body diagrams. Start with the mass m. What forces are acting on m?


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