Analysis and solution: Because the glass is cylindrical, after the plumb hammer is taken out, the falling part of the water surface is actually a small cylinder. The bottom of this cylinder, like the bottom of glass, is a circle with a diameter of 20 cm, and its volume is exactly equal to that of the cone plumb hammer. The height of this small cylinder is the height of the water falling.

Because the volume of conical plumb hammer is

V= 1/3×π(6/2)^2×20=60π

Let the height of the water level drop be x, then the volume of the small cylinder is x(20÷2)2×x= 100πx (cubic centimeter).

So there is the following equation:

60π= 100πx, to solve this equation:

X=0.6 cm

A: After the plumb hammer was taken out, the water level in the cup dropped by 0.6 cm.