A dockworker loading crates on a ship finds that a 26-kg crate, initially at rest on a horizontal surface, requires a 72-N horizontal force to set it in motion. However, after the crate is in motion, a horizontal force of 54 N is required to keep it moving with a constant speed. Find the coefficients of static and kinetic friction between crate and floor. g

Explanation:

A 26-kg crate, initially at rest on a horizontal surface, requires a 72-N horizontal force to set it in motion.

Maximum Frictional force on stationary object  F = μs R  where μs is coefficient of static friction and R is reaction of ground which is equal to weight for object placed on horizontal surface .

F = μs  x mg

Given F = 72 , m = 26

72 = 26 x 9.8 x  μs

μs = .28

Kinetic friction : ---

Frictional force on moving  object  F = μk R  where μk is coefficient of kinetic friction and R is reaction of ground which is equal to weight for object placed on horizontal surface .

F = μk  x mg

Given F = 72 , m = 26

54 = 26 x 9.8 x  μk

μk = .21  

i would say