A 5.0 kg box is placed on a flat surface and pushed with a horizontal force of 20 N. If the coefficient of static friction between the box and the surface is 0.4, what is the maximum force of static friction acting on the box?

Core Concept

The maximum force of static friction can be calculated using the formula f_s(max) = μ_s × N, where μ_s is the coefficient of static friction and N is the normal force. In this case, the normal force equals the weight of the box (mg = 5.0 kg × 9.8 m/s² = 49 N). Therefore, f_s(max) = 0.4 × 49 N = 19.6 N. Option A is incorrect because there is friction present. Option C is incorrect because the applied force (20 N) is greater than the maximum static friction, but this doesn't determine the friction force. Option D is incorrect because it uses the weight directly without multiplying by the coefficient.