Body of mass m is being pulled by a string so that it moves horizontally at constant speed.
Friction coefficient between surface and body is u.Find an angle (alpha) between a string and horizontal surface for which tension in string is minimal and find that tension.
weight w=mg ; n=normal force
acceleration due x-axis=0
The Attempt at a Solution
\sum F_y=Tsin(\alpha)+n+(-w)=0; \\
\sum F_x=Tcos(\alpha)+(-f)=0 \\
\sum F_x=Tcos(\alpha)+(-un)=0; \: Tcos\alpha=un ; \\
Now I'm not sure what to do next.I need to find minimal angle so derivative of the last expression should be zerr should I differentiate arctan?I'm confused.[/B]