A cube of oak wood with very smooth faces normally floats in water. Suppose you submerge it completely and press one face flat against the bottom of a tank so that no water is under that face. Will the block float to the surface? Is there a buoyant force on it? Explain

There is no Buoyant force.

The block will only float to the surface when the pressed face is released

Explanation:

There would be no Buoyancy force on the cube of Oak wood when one face is pressed flat against the Bottom of a tank and this is simply because there is no upward force acting on the side of the cube that is pressed against the bottom

Buoyant force is simply caused by the pressure difference between the water over and under an object immersed in water . hence since there is no water pressure under the immersed cube there will be no pressure difference between the water under and over the cube of oak wood immersed in the water.

c. magnitude and direction

+15-35=-20

going in opposite directions