Question

a box being pushed with a force of 85N right slides along the floor with a constant speed of 0.5m/s. What is the force of sliding friction on the box?

Answer 1

`85\; \rm N`.

Step-by-step explanation:

The box is sliding with a constant speed in a fixed direction (to the right.) In other words the velocity of this box is constant. Hence, this box would be in a translational equilibrium. The acceleration of this box would be zero.

By Newton's Second Law of motion, the net force on this box would be
`0`. In other words, forces on this box are balanced.

The question is asking for the size of the friction on the box. Assuming that the floor is horizontal. The friction on this box would also be horizontal,

The only other force that could balance that friction would be the
`85\; \rm N` push to the right. The direction of this push is horizontal (to the right.) Hence, the entirety of that
`85\; \rm N\!` would be in the horizontal direction.

Thus, forces on this box in the horizontal direction would be:

• The
  `85\; \rm N` push to the right.
• Friction that opposes the rightward motion of the box (that is, to the left.)

Since these two forces must balance each other, the size of the friction would also be
`85\; \rm N`.