Final answer:
In the presence of a uniform electric field, free electrons in the copper cube move to counteract the field, leading to a redistribution of surface charge that cancels the internal field, likely resulting in a negative charge on the bottom surface.
Step-by-step explanation:
The charge on the bottom surface of a solid copper cube resting on a wooden table in a region with a uniform external electric field directed straight upward can be discussed in terms of the behavior of charges in conductors and the concept of electric flux. When an external electric field is applied to a conductor such as copper, the free electrons in the metal will move to counteract the field. This redistribution of charges creates an induced electric field within the conductor that opposes the external electric field. As a result, there will be a redistribution of charges on the surface of the copper cube.
In electrostatic equilibrium, the electric field inside the conductor is zero. The charges on the surface of the cube arrange themselves so that the electric field inside is canceled out. For the cube resting on the wooden table, we can infer that the charges on the bottom surface will accumulate in such a way that they will oppose the upward electric field, likely leading to a negative charge distribution on the bottom surface that counters the upward field. The net electric flux through the cube in a uniform field is zero, as discussed in physics textbooks, since the cube will not alter the field lines passing through it, and flux through its sides perpendicular to the field is zero.