Question

Graph between frictional force and applied force is given below. Choose the correct statement among the following

• A. Frictional force is directly proportional to the applied force is shown by region $CD$
• B. Frictional force is maximum in region $CD$
• C. Frictional force is directly proportional to the applied force is shown by region $AB$
• D. Region $AB$ is showing dynamic friction and $CD$ is showing static friction

Answer 1

The correct option is C Frictional force is directly proportional to the applied force is shown by region $AB$

When a force is applied to an object lying on a rough surface, a resisting force comes into existence which is static friction and it is a self adjusting force as it increases with applied force till it reaches the value of limiting friction which is the maximum force it can resist.
After this if applied force keeps on increasing suddenly the object starts moving and the value of resisting friction force decreases and continues with a constant value of friction, at this stage it is known as Kinetic friction.
Kinetic friction has a constant value but little less than Limiting friction. So, in the given graph region AB is the Static friction region which is directly proportional to the applied force and point B represents the point of limiting friction. And region $BC$ is a sudden drop down in the value of friction when the object will start its motion from rest. And the region $CD$ represents kinetic friction which occurs when an object is in motion and it has a constant value hence $CD$ is a straight line. So, from options, option (3) correctly fits the above explanation.