A box is dragged without acceleration in a straight-line path across a level surface by a force of 13 N. What is the frictional force between the box and the surface?

13N

Explanation:

Since the body being dragged across the surface is not accelerating, the acceleration of the body is 0m/s².

Note that frictional force is a force of opposition i. e it opposes the motion of an object.

From Newtons second law of motion, F = ma where;

F is the sum of the forces acting on the body

m is the mass of the body

a is the acceleration

If the box is dragged along a leveled surface by a force of 13N, its moving force (Fm) is 13N and the frictional force (Ff) will act opposite to this force.

Resultant force acting on the box along the horizontal will be Fm + (-Ff)

Therefore;

Fm + (-Ff) = ma

Fm-Ff = ma

Since a = 0m/s²

Fm-Ff = m (0)

Fm-Ff = 0

Fm = Ff

This shows that for a static body, the moving force acting on the body will be the same as the frictional force. Since Fm = 13N

Frictional force (Ff) = 13N

Therefore, the frictional force between the box and the surface is 13N