Question

What is the value of sliding friction for an object which requires $7N$ of force to move it from rest?
\[(A)7N\]
$(B){\text{Greaterthan}}7N$
$(C){\text{Lessthan}}7N$
$(D)14N$

Answer 1

Hint: Sliding friction is defined as the constraints that occur between any two objects when they are sliding against each other. Static friction is represented as the frictional force that occurs between the surfaces when they are at rest concerning each other.
For a given two planes, sliding friction is a little lesser than that of static friction because it is not tougher to move the object which is already in motion than the object which is at rest.

Complete step-by-step solution:
Sliding friction is less than the friction that is created before sliding, i.e., static friction. Static friction is not more than and that's why sliding friction is less than $7N$. For a given two planes, sliding friction is a little lesser than that of static friction because it is not tougher to move the object which is already in motion than the object which is at rest.
Here in the problem, it is given that the object needs $7N$ force to move from the rest. That means the maximum value of the static friction here is $7N$.
Now if we consider the given options:
\[(A)7N\]: this value is equal to the maximum static friction which can't be true because the sliding friction should be less than the static friction.
$(B){\text{Greater than }}7N$: this option states that the sliding friction is greater than the maximum static friction which can't be true because the sliding friction should be less than the static friction.
$(C){\text{Less than }}7N$: this option states that the sliding friction is less than the maximum static friction, hence this option is true.
$(D)14N$: this value is equal to twice the maximum static friction which can't be true because the sliding friction should be less than the static friction.
Hence the right answer is in option (C).

Note:We can state the limiting friction as the highest value of static frictional force that occurs when a body is just at the point of sliding from the surface of another body. Limiting friction is gained by multiplying the normal force and the coefficient of limiting friction. When the body overcomes the force of static friction, the highest value of static friction is gained knowing as limiting friction. After the limiting friction, the force due to friction is not going to increase anymore.