Force Problem Homework: Calculating Mass and Friction Coefficient

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The discussion revolves around a physics homework problem involving two masses, friction, and acceleration. The larger mass is 2.4 times the smaller mass, with a friction coefficient of 0.35. To maintain an acceleration of 4.0 m/s², participants are trying to determine the necessary applied force and the minimum static friction coefficient to prevent slipping of the smaller block. There is confusion regarding the net force equations and how to derive the applied force needed for the given acceleration. The recommendation is to work symbolically to simplify the problem-solving process and clarify potential errors.
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Homework Statement



A mass "b" is placed on top of a larger mass that is 2.4 times the mass of the smaller one as shown. The coefficient of friction between the larger block and the surface is 0.35. A horizontal force acts on the larger block.

a) What force would be necessary to maintain an acceleration of 4.0 m/s2? (in terms of "b")
b) What would be the minimum coefficient of static friction necessary to keep the smaller block from slipping?

Homework Equations



a = Fnet / m
Ff = µFN
Fnetx = Fa + Ff
Fnety = Fg + FN

The Attempt at a Solution



Fg = ma
Fg = 3.4b (9.81)
Fg= 33.354b N [down]

Fnety = Fg + FN
0 = 33.354 N [down] + FN
FN = 33.354b N [up]

Ff = µFN
Ff = (0.35)(33.354b N)
Ff = 11.6738b N

Fnetx= Fa + 11.6738b N

I don't know how to get Fnetx from here, and I don't know if this is right so far4.0 m/s2= Fnet / 3.4b

Also I don't understand part b)
Thanks for the help
 
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anon1 said:
Fnetx = Fa + Ff
No, Fnetx = Fa. You want to find Fapp, where Fnetx = ƩF = Fapp + Ff.
Also I don't understand part b)
The smaller mass is to accelerate at 4m/s2. What force is necessary to achieve that? Where is that force coming from?

Btw, I recommend working entirely symbolically, only plugging in numbers when you get to the final equation. It makes it easier to find errors, and much easier for others to follow.
 
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