Question

A crate weighing 490 N is pushed along a surface. If it takes 126 N to get the crate starts to move (a = 0), what is its static friction and coefficient of static friction μ_s? Solve the unknown and confirm your answer of static friction using the Phet Simulation software. (Use the part of with Acceleration in Phet Simulation)

Answer 1

The static friction force by definition

$$F_f=\mu_sN=\mu_s mg$$

The static friction force

$$F_f=F=\rm 126\: N$$

The static friction coefficient

$$\mu_s=\frac{F_f}{mg}=\frac{126}{490}=0.257$$