Answer: Solution: According to the stress analysis of the frame ABC, its overall center of gravity is at point O, and from the mathematical knowledge, OD= 13CD.

If the frame ABC is in equilibrium, the moment of gravity should be equal to the moment of F, and F is balanced according to the moment:

f？ CD=3mg？ mean sea level

Solution: F = mg

Turn the frame counterclockwise from the position shown. When the moment of f' is equal to the moment of gravity in motion, the kinetic energy is the largest.

Yes: F'l=3mg? L

Solution: L= 12l,

That is, when the distance from the center of gravity to the wall is 12l, the kinetic energy is the largest. According to the geometric relationship, the rotation center angle θ=π6.

Force f's work in this process is:

w = F′lθ= 1.5 mgl×π6 = 0.25πmgl

So the answer is: mg, 0.25πmgl.