(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

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.

2. Relevant equations

[tex]\Sigma[/tex]F = ma

F_{fr}= [tex]\mu[/tex]F_{N}

3. The attempt at a solution

FBD

http://img255.imageshack.us/img255/2181/forceandnewtonaccelerat.jpg [Broken]

Net Force Equations

[tex]\Sigma[/tex]F_{y}= ma

F_{N}- F_{G}= ma

F_{N}- mg = ma

F_{N}= mg + ma

Acceleration is 0 because the box is not moving up or down so

F_{N}= mg

[tex]\Sigma[/tex]F_{x}= ma

F_{app}cos[tex]\theta[/tex] - F_{fr}= ma

F_{app}cos[tex]\theta[/tex] - [tex]\mu[/tex]F_{N}= ma

F_{app}cos[tex]\theta[/tex] - [tex]\mu[/tex]mg = ma

(F_{app}cos[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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# Forces and Newton-Identifying Acceleration

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