Question

A person pushes a desk across the horizontal floor with a constant force of $20.0N$. The desk moves at a constant velocity of $2.0m/s$. If the only other horizontal force acting on the desk is the force of friction. How does the amount of frictional force compare to the amount of force the person applies?

• A. The force of friction must be greater than the force the person applies.
• B. The force of friction must be less than the force the person applies.
• C. The force of friction must be the same as the force the person applies.
• D. The force of friction must be zero.
• E. Not enough information is given to answer this question.

Answer 1

Answer: (C)

The force of friction must be the same as the force the person applies.

As the velocity of the desk is constant , therefore acceleration of the desk is zero ($a=0$) hence net force on the desk is also zero (by $F=ma$) , it implies that force of friction must be the same as the force the person applies .