Question

ASSERTION: A sphere cannot roll on a smooth inclined surface.
 REASON: For a smooth inclined surface force of friction is equal to zero.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Assertion is incorrect but Reason is correct

Answer 1

Hint: For rolling motion to occur there must exist some frictional force called rolling frictional force which will prevent slipping of the object down the plane. If the force of friction is zero or negligible the object will not roll. In absence of friction the object will slip down the plane.

Complete answer:
Whenever a body moves or tends to move over the surface of another body, a force comes into play which acts parallel to the surface of contact and opposes the relative motion. This opposing force is called friction.

Due to friction a sphere rolling down a surface will not slip and continue its motion. If there is no friction then the sphere will not roll, the sphere will slip down the plane.

For a smooth inclined surface the force due to friction is zero so a sphere cannot roll on a smooth inclined plane because for a smooth inclined plane the force of friction is zero.
So the assertion is correct and reason is also the correct explanation for assertion.

So, the correct answer is “Option A”.

Additional Information:
The friction is a result of contact force. Because when two bodies are placed in contact attractive forces act between their particles at the surface of contact. As a result, each body exerts a contact force on the other. These mutual contact forces are equal and opposite obeying Newton’s third law. The component of contact force acting normal to the contact surface is called normal force or normal reaction and the component parallel to the contact surface is called friction.

Note:
The friction is of different types.

a.)Static friction: It is the force of friction that comes into play between two bodies before one body actually starts moving over the other. Static friction opposes the impending motion. As the force increases the force of friction increases to a maximum value.

b.)Limiting friction: the maximum force of static friction which comes into play when a body just starts moving over the surface of another body is called limiting friction.

c.)Kinetic friction: the force of friction which comes into play when a body is in a steady motion over the surface of another body is called kinetic or dynamic friction.