uppose the bottom block has a mass of 0.4 kg and the top block has a mass of 0.1 kg. What force do you need to exert (in newtons) to keep the blocks moving at a constant speed of 10 cm/s

F = 0

Explanation:

Newton's second law is

F = ma

As in this case the two blocks move with constant speed, it implies that the acceleration is zero, therefore the force applied to the system is zero

F = 0