In the horizontal smooth tube there is a circular bend of radius$r=10m$ located in the vertical plane. What is the minimum speed (in m/s)to be given to thin flexible rope of $length L=4\pi r$ horizontal position so that it just crosses the circular bend and again become horizontal? Consider the radius of the loop r is much larger than the radii of the pipe and rope and the rope was initially in left horizontal section. [Take $g=10m/s^2$]