A dock worker loading crates on a ship ﬁnds that a 29 kg crate, initially at rest on a horizontal surface, requires a 90 N horizontal force to set it in motion. However, after the crate is in motion, a horizontal force of 60 N is required to keep it moving with a constant speed. The acceleration of gravity is 9.8 m/s^2

Question

A dock worker loading crates on a ship ﬁnds that a 29 kg crate, initially at rest on a horizontal surface, requires a 90 N horizontal force to set it in motion. However, after the crate is in motion, a horizontal force of 60 N is required to keep it moving with a constant speed. The acceleration of gravity is 9.8 m/s^2 
Find the coeﬃcient of static friction be- tween the crate and ﬂoor.

Henry · Answer

Fc = m*g = 29kg * 9.8N/kg = 284.2 N. = Force of crate. Fap-Fs = m*a 90-u*Fc = m*0 90 - u*284.2 = 0 u*284.2 = 90 us = 0.317