Question

A plate of 1 kg sits on a counter. The coefficient of static friction is 0.25 and the coefficient of kinetic friction is 0.15. If a horizontal force of 20N is applied on the place, what is the magnitude of force due to friction on the plate?

Answer 1

Calculate the magnitude of force of friction of a resting and moving plate:

$$f_s=\mu_smg=2.45\text{ N}.\\ f_k=\mu_kmg=1.47\text{ N}.$$

2.45 N is the force that is required to make the plate move. Since 20 N is greater than 2.45, the plate will move with the force of friction of 1.47 N.