Sir, please help me with one more question which is mentioned below:-

the answer would be 400/sqrt(91)

basically, you will have to transform the cone into a circular arc and then use the fact that shortest distance between A and B would be a straight line. note that the arcs angle wwould be 120 deg or 2pi/3. then, use cosine rule to determine length of AB, which you can find out to be AB= 10sqrt(91). further, note that downhill portion will start to the left of the perpendicular dropped from the centre of circular arc. so, again use pythagoras theorem to find out the length of this portion= 400/sqrt(91)