- #1
ciubba
- 65
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Homework Statement
Body A in Fig. 6-33 weighs 102 N, and body B weighs 32 N. The coefficients of friction between A and the incline are μs 0.56 and μk 0.25. Angle θ is 40. Let the positive direction of an x-axis be up the incline. In unit-vector notation, what is the acceleration of A if A is initially (a) at rest, (b) moving up the incline, and (c) moving down
the incline?
Free body diagram: http://postimg.org/image/fh6livrer/
See attached picture (problem 27)
http://postimg.org/image/5svunp27z/
Homework Equations
Fnet=ma
The Attempt at a Solution
Clearly the answer to part a is 0-- I'm stuck on part b.
For B, [tex] F_{Net, y}= -m_B a_y = F_T -m_B g \rightarrow F_T = m_B g - m a_y[/tex]
For A, [tex] F_{Net, x}=ma_x = - \mu _k m_A g cos(40) +F_T - m_A g sin(40)[/tex]
Plugging in the information,
[tex] 102 a= -0.25*102*cos(40)+32-32a -102sin(40) \rightarrow a=-.39[/tex]
However, the book lists the correct answer as -3.9, so I'm off by a power of ten. Where did I go wrong?