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myxomatosii
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Homework Statement
Two packages at UPS start sliding down the 20° ramp shown in Figure P8.25. Package A has a mass of 5.0 kg and a *coefficient of friction of 0.20. Package B has a mass of 10 kg and a coefficient of friction of 0.15. How long does it take package A to reach the bottom?
I call the larger mass m2 and the smaller mass m1.
http://img166.imageshack.us/img166/1899/p825.gif
Homework Equations
F=ma
fk=μkn
The Attempt at a Solution
I have drawn two free body diagrams.
m1
up: n1
down:m1gCos(θ)
left:F2 on 1 , m1gSin(θ)
right: fk1
m2
up: n2
down: m2gCos(θ)
left: m2gSin(θ)
right:F1 on 2 , fk2
From this I wrote.
Σ μ θ
ΣFx1=fk1-F2 on 1-m1gSin(θ) = m1ax1
ΣFy1=n1-m1gCos(θ)
therefore
n1=m1gCos(θ)
ΣFx2=F1 on 2+fk2-m2gSin(θ)=m2ax2
ΣFy2=n2-m2gCos(θ)
therefore
n2=m2gCos(θ)
Now where to go from here? I am not sure but I believe I need to find the acceleration of the system since both are bound together by this law. By finding that I would then know ax1 and ax2.
I'm just not sure how... two different μk confuse me, how can I find the total acceleration of the system if both are dragged by different coefficients?
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