
Answer:
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 Â