Final answer:
The question requires using physics principles to calculate the forces of static and kinetic friction acting on a crate based on its mass, the applied forces, and the coefficients of friction.
Step-by-step explanation:
The question involves the concepts of static and kinetic friction, force, mass, acceleration, and coefficient of friction. Physics equations and principles are used to solve these types of problems. When an object like a crate is in contact with a surface, frictional forces act on it. The maximum static frictional force can be calculated by multiplying the coefficient of static friction by the normal force. Once an object is in motion, kinetic friction comes into play, which is usually less than static friction. The coefficient of kinetic friction is used in similar calculations for an object that is sliding. Both coefficients are unitless and describe the frictional properties of the materials in contact.
For example, if a 20.0-kg crate is on a flat surface with a coefficient of static friction of 0.700, the maximum static frictional force is calculated using the crate's weight (which is the normal force) and the coefficient of static friction. If different forces are applied to the crate, the force of friction adjusts up to the maximum static frictional force, unless the applied force exceeds it, at which point the crate will start to move and kinetic friction applies.