A tired worker pushes a heavy (100-kg) crate that is resting on a thick pile carpet. The coefficients of static and kinetic friction are 0.6 and 0.4, respectively. The worker pushes with a horizontal force of 490 N. The frictional force exerted by the surface is

The friction force exerted by the surface is 490 newtons.

Explanation:

From Physics, we remember that static friction force (), measured in newtons, for a particle on a horizontal surface is represented by the following inequation:

(Eq. 1)

Where:

- Static coefficient of friction, dimensionless.

- Mass of the crate, measured in kilograms.

- Gravitational acceleration, measured in meters per square second.

If , then crate will experiment an imminent motion. The maximum static friction force is:  (, , )

From Newton's Laws we get that current force of friction as reaction to the pulling force done by the worker on the crate is:

(Eq. 2)

Where:

- Horizontal force done by the worker, measured in newtons.

- Static friction force, measured in newtons.

If , then the static friction force exerted by the surface is:

Given that , the crate does not change its state of motion. The friction force exerted by the surface is 490 newtons.