- #1
KillerZ
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Homework Statement
Determine the acceleration of block A when the system is released. The coefficient of kinetic friction and the weight of each block are indicated. Neglect the mass of the pulley and cord.
Homework Equations
[tex]\sum F = ma[/tex]
The Attempt at a Solution
[tex]w_{B} = 20 lb[/tex]
[tex]w_{A} = 80 lb[/tex]
[tex]\mu_{k} = 0.2[/tex]
[tex]\theta = 60 deg[/tex]
Block A
[tex]\leftarrow\sum F_{x} = ma_{x}[/tex]
[tex]-F_{f}cos60 + Nsin60 - 2Tcos60 = ma_{x}[/tex]
[tex]\downarrow\sum F_{y} = ma_{y}[/tex]
[tex]-F_{f}sin60 + w - Ncos60 - 2Tsin60 = ma_{y}[/tex]
Block B
[tex]\downarrow\sum F_{y} = ma_{y}[/tex]
[tex] w - T = ma_{y}[/tex]
Kinematics
[tex]2S_{A} + S_{B}[/tex]
[tex]2a_{A} + a_{B}[/tex]
[tex]a_{A} = -\frac{a_{B}}{2}[/tex]
I am confused do I just say [tex]N = ma = (\frac{80lb}{32.2ft/s^{2}})(32.2ft/s^{2})[/tex] or do I have to solve N as an unknown?
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