Explanation:
As the skateboarder wants to cross the play ground . The surface is rough .
As we know , the force of friction is non-conservative force . Thus work is required against this force .
We have formula:
work done = Force x distance (in one direction )
Te force applied cannot be changed , so he is to decrease the distance .
In case of circle , diameter is the minimum distance . Thus he is supposed to move along it .