Question

Using a horizontal force of 200N, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?

Answer 1

Hint: First draw a free body diagram, show all the forces in the diagram with direction and apply force balance on man and plank.

Complete step by step answer:
Free body diagram for wooden cabinet

Here, f is frictional force.
When velocity is constant then change in velocity is zero. It means acceleration is zero because acceleration is change in velocity per unit time. And if acceleration is zero the only two forces will act on the wooden cabinet, one is 200N and other is friction force.
Force balance on wooden cabinet
$\begin{align}
  & f=F \\
 & f=200N \\
\end{align}$

Additional information:
Frictional force – it is the force generated by two surfaces that contact and slide against each other. Frictional force offers the resistance to the applied force opposing its motion. Frictional force always acts in the opposite direction to that of the object in motion and tries to stop the body.

Note: Always use force balance, do not solve this type of questions without drawing free body diagrams. In the laws of motion chapter, students should first draw the free body diagram and find how many forces are acting on a body from all the directions.