A body weighing 10 kg moves uniformly rectilinearly on a horizontal surface under the action

A body weighing 10 kg moves uniformly rectilinearly on a horizontal surface under the action of a force of 20 N directed horizontally on it. What is the value of the coefficient of friction?

Since a body of mass m moves uniformly, its acceleration along the horizontal surface a is zero, which means that the resultant F of the forces applied to it is also zero:

a = F / m = 0;

F = 0.

Along the horizontal surface, the body is acted upon by the traction force Ft and the friction force Ffr, the directions of which are opposite. Since their resultant is zero, then

Ft = Ftr.

The friction force can be found by the formula

Ftr = f * N.

Since in the vertical plane only gravity is acting on the body, equal to m * g and directed downward, and the reaction force of the support N, directed upward, and the body does not move vertically, then

N = m * g.

Then

Ftr = f * m * g;

Ft = Ftr = f * m * g,

whence the coefficient of friction is

f = Ft / (m * g);

f = 20 / (10 * 10) = 0.2.