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Homework Statement
A man pulls a rope, with a force of 200N, attached to a box, with a mass of 35kg, 30° from the horizontal. The [tex]\mu[/tex]k is 0.3. Find the acceleration of the box.
Homework Equations
[tex]\Sigma[/tex]F = ma
Ffr = [tex]\mu[/tex]FN
The Attempt at a Solution
FBD
http://img255.imageshack.us/img255/2181/forceandNewtonaccelerat.jpg
Net Force Equations
[tex]\Sigma[/tex]Fy = ma
FN - FG = ma
FN - mg = ma
FN = mg + ma
Acceleration is 0 because the box is not moving up or down so
FN = mg
[tex]\Sigma[/tex]Fx = ma
Fappcos[tex]\theta[/tex] - Ffr = ma
Fappcos[tex]\theta[/tex] - [tex]\mu[/tex]FN = ma
Fappcos[tex]\theta[/tex] - [tex]\mu[/tex]mg = ma
(Fappcos[tex]\theta[/tex] - [tex]\mu[/tex]mg) / m = a
((200N)(cos30°) - (0.3)(35kg)(9.8m/s²)) / 35kg = a
2.0087m/s² [tex]\approx[/tex] a
I am told this is wrong and that the correct answer is around 2.87m/s².
What did I do wrong so that I did not arrive at the correct answer?
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