Question

A body of weight 50N is placed on a smooth surface. If the force required to move the body on the surface is 30N the coefficient of friction is
A.0.60
B.1.2
C.0.3
D.1.67

Answer 1

Hint: To solve this problem, we have to use the formula for friction force. Friction force is coefficient of friction times the normal force. Thus, the coefficient of friction is the ratio of friction force to the normal force with no motion. Hence, take the ratio of forces, substitute the values and the value obtained will be the coefficient of friction.
Formula used:
$ f=\mu N$

Complete answer:
Given: Friction force (f)= 30N
            Normal force (N)=50N
The formula for Friction Force is given by,
$ f=\mu N$ …(1)
Where, $\mu$ is the coefficient of friction
            N is the normal force
Substituting the values in the equation...(1) we get,
$ 30=\mu \times 50$
$\mu =\dfrac { 30 }{ 50 }$
$\Rightarrow \mu =0.6$
Thus, the coefficient of friction is 0.6.


Hence, the correct answer is option A i.e. 0.6.

Additional Information:
When the friction is stronger than the normal force, the coefficient of friction is greater than 1. Silicon rubber is an example for objects with coefficients of friction greater than 1. The value of co-efficient is generally between 0 and l but it can be greater than 1,

Note:
Students have to remember the formula for friction force to solve such problems. Students have to keep in mind that the coefficient of friction is ratio of forces. Hence, it is a unit less and dimensionless quantity. Coefficient of friction depends upon the heaviness of the material and roughness of the material. Normal force is perpendicular to the applied force. Friction force acts in the opposite direction of the actual motion but parallel to the surface.