An object with mass m is given initial velocity to slide across a horizontal plane AB towards a semi circle BCD with radius R.
Between the object and the plane exists a kinetic friction u_k=0.5, but only between the section FB with length R. F is in the middle of A and B. The inside of the circle is smooth.
When the object reached to point C, it applies a force of 3mg on the semi circle.

The object is going to the left.

1. Write an expression for the initial velocity at point A.