NCERT Question 10 - Chapter 9 Class 9 - Force and Laws Of Motion

Using a horizontal force of 200 N, 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

Since we move the cabinet with constant velocity, its acceleration will be 0.

Since acceleration is 0, no net force will be applied to it.

So, Total Force on body = 0

Now, Total Force on body will be the force applied and Friction.

Thus,

Force on body + Friction = 0

200 N + Friction = 0

Friction = 0 - 200

Friction = -200 N

Negative sign of force means that the force is applied in the opposite direction of motion