Question

1. Apply a constant force of 50 N directed to the right of the 50 kg Box. (2 pts)

Answer 1

As the box is moving with a constant velocity, the two forces acting on the box are canceling each other.

Then   friction force = 80 Newtons              but in the opposite direction.

Friction force =  Mu  * Normal force exerted by ground  =  Mu * weight of box

So we find Mu.

Mu = coefficient of friction between box and horizontal surface

          = Force of friction / weight  =  80 / 50 * 9.81 = 0.163

When an identical box is placed on top, the force of friction is

      = Mu * total weight = 0.163 * (50+50) * 9.81 = 159.9 Newtons