Question

A solid homogeneous sphere is moving on a rough horizontal surface, partly rolling and partly sliding. During this kind of motion of this sphere :

• A. total kinetic energy is conserved
• B. angular momentum of the sphere about the point of contact with the plane is conserved
• C. only the rotational kinetic energy about the centre of mass is conserved.
• D. angular momentum about the centre of mass is conserved.

Answer 1

The correct option is B angular momentum of the sphere about the point of contact with the plane is conserved

At the point of contact the frictional force acts tangentially and the weight of the sphere pass through it perpendicularly and there is no other force acting on the sphere . So,as the all forces passing through the point of contact , the moment of all forces acting on the body about point of contact is zero. Hence there is no torque about point of contact which means angular momentum about point of contact must be conserved.