A dockworker loading crates on a ship finds that a 21-kg crate, initially at rest on a horizontal surface, requires a 70-N horizontal force to set it in motion. However, after the crate is in motion, a horizontal force of 51 N is required to keep it moving with a constant speed. Find the coefficients of static and kinetic friction between crate and floor.

Question

A dockworker loading crates on a ship finds that a 21-kg crate, initially at rest on a horizontal surface, requires a 70-N horizontal force to set it in motion. However, after the crate is in motion, a horizontal force of 51 N is required to keep it moving with a constant speed. Find the coefficients of static and kinetic friction between crate and floor.
μstatic    	 
μkinetic

bobpursley · Answer

initial friction=70N=coeff_s*mass*g solve for coeff_s sliding friction friction=51N=coeff_k*mass*g