The wizard has a mass of 80 kg and sits 3 m from the center of a rotating platform. Due to the rotation his speed is increased from rest by [itex]\dot{v}\,=\,0.4\,\frac{m}{s^2}[/itex]. If the coefficient of static friction between his clothes and the platform is [itex]\mu_s\,=\,0.3[/itex], determine the time requiredto cause him to slip.(adsbygoogle = window.adsbygoogle || []).push({});

http://img150.imageshack.us/img150/1639/problem13784pt.jpg [Broken]

Here is what I have, it is off by 0.4 seconds though:

http://img150.imageshack.us/img150/8531/problem1378fbd4za.jpg [Broken]

[tex]\sum\,F_y\,=\,N\,-\,W\,=\,m\,a_y\,\Rightarrow\,N\,=\,W[/tex]

[tex]N\,=\,784.8N[/tex]

[tex]\sum\,F_x\,=\,f_s\,=\,m\,a_x\,\Rightarrow\,\mu_s\,N\,=\,m\,a_x[/tex]

[tex]a_x\,=\,\frac{\mu_s\,N}{m}\,=\,\frac{(0.3)\,(785\,N)}{80\,kg}\,=\,2.94\,\frac{m}{s^2}[/tex]

[tex]t_{slip}\,=\,\frac{a_x}{\dot{v}}\,=\,\frac{2.94\,\frac{m}{s^2}}{0.4\,\frac{m}{s^2}}\,=\,7.35[/tex]

The book has 7.39s and the units don't match!

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# Homework Help: A wizard sits 3 m from the center of a rotating platform, coeefficient of static fric

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