Awooden box weighing 150 n is sliding at a constant rate over a concrete sidewalk. the force required to pull the box at a steady rate is 78 n. what is the coefficient of friction?
1.9
228
72
0.52

0.52

Explanation:

The box is moving at constant velocity along the horizontal direction: this means that its acceleration is zero. According to Newton's second law:

where is the net force acting on the object, m its mass, and a its acceleration, since the acceleration is zero, then the net force must be zero as well.

There are in total 4 forces acting on the box:

- along the vertical direction: the weight of the box (downward), given by , and the normal reaction of the floor on the box (upward),

- along the horizontal direction: the force that pulls the box, , and the frictional force, which is given by , in the opposite direction

Since the net force is zero, the resultant on each direction must be zero. In the vertical direction we have:

While in the horizontal direction we have

So, the coefficient of friction is 0.52.