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

object 2 because all the other ones are wrong

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg