二、計算題
1. A baseball player knows the fact that when he hits a baseball on the so called "sweet spot", the ball can get a maximum momentum to fly away. Strangely, the baseball player can feel almost no force exerted from this perfect hit. Based on the above no force exerted statement and using a uniform stick with length L to model a baseball bat, find the sweet spot on this stick. You should assume the baseball player holding the bat at its one end and the swing of the bat is like a rotation about this end.