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Homework Statement
http://streetrodjohn.home.comcast.net/~streetrodjohn/physics.jpg
A 1-kg block is pushed against a 4-kg block on a horizontal surface of coefficient of friction 0.25, as shown in the figure. Determine the minimum force needed to ensure that the 1-kg block does not slip down. Assume that the coefficient of friction at the interface between the block is 0.4. Hint: The two blocks exert equal and opposite forces on each other.
Homework Equations
F=(A+B)a
Ag=fs
N=Ba
Ag=[tex]\mu[/tex]Ba
The Attempt at a Solution
In class we have done similar problems, only with a frictionless horizontal surface. I don't know how to account for the horizontal coefficient of friction of .25 in this problem. Using the above equations and ignoring the horizontal coefficient of friction, I get this:
a=(Ag)/([tex]\mu[/tex]B
F=(((A+B)Ag)/([tex]\mu[/tex]B))
F=(((4+1)(1)(9.8))/((.4)(4)))
F=30.62N
Now how do I account for the horizontal coefficient of friction of .25? Thanks in advance for any help you can provide.
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