A force of 18 N is applied horizontally to a 40 kg mass on a horizontal floor, causing it to accelerate at 0.3 m/s². Given g = 10 m/s², find the coefficient of kinetic friction.

• Applied Force ($F_A$) = $18 \text{ N}$
• Mass ($m$) = $40 \text{ kg}$
• Acceleration ($a$) = $0.3 \text{ m/s}^2$
• Acceleration due to gravity ($g$) = $10 \text{ m/s}^2$ (commonly used in such problems for simplicity, and it leads to one of the options exactly).

Since the mass is on a horizontal floor, the normal force is equal to the gravitational force (weight) acting on the mass.

The net force in the horizontal direction is the applied force minus the frictional force, and this net force causes the acceleration.

Now, solve for $F_f$:

The frictional force is related to the normal force by the coefficient of friction:

Rearrange to solve for $\mu$:

The final answer is $\text{B) } 0.015$.