posted by Hello .
A 2.5 wood block is pulled along a wood floor at a steady speed. A second wood block, with mass 3.5 , is attached to the first by a horizontal string. what is the magnitude of the force pulling on the first block
That depends upon the force needed to pull the first block, before the second block was added.
It also depends upon whether the two blocks are still being pulled at constant speed.
Presumably the force is needed to overcome friction. If the same kind of wood is in contact in the second block, the required force increases by a factor 6/2.5 = 2.4
Joe the plumber, you are a god.