A block with a mass of 20 kg moves towards the east at a constant velocity across a rough horizontal surface, as shown in the diagram below - NSC Technical Sciences - Question 1 - 2022 - Paper 1

The velocity of the block is constant, which implies that there is no net force acting on it. According to Newton's first law, if the net external force is zero, the acceleration of the object must also be zero. Therefore, the correct explanation is that the applied force $F_{app}$ equals the frictional force $F_r$, and thus the acceleration $a$ is zero. The correct choice from the options provided is:

Answer: B $F_{app} < F_r$ and $a = 0 ext{ m/s}^2$.