The motion of a sphere moving on a rough horizontal surface changes from pure sliding to pure rolling. In this process, the force of friction:
(a)initially acts opp to motion and then in direction of motion
(b)causes linear retardation
(c) causes angular acceleration
(d) stops acting acting when pure rolling begins.
This is a multi correct answer type question.
The answer given is (b,c,d). This is what I could think about:
The rolling must require a driving force and that is provided by friction. So friction must be there initially. But for the sphere to rotate and slide, friction must be opposing linear motion. So friction causes linear retardation and angular acceleration. And friction opposes the direction of motion as long as it is acting in this case.
So b,c,d looks fine. But then why doesn't the sphere start rolling as soon as it starts moving?