Question: A sphere $S$ rolls without slipping, moving with a constant speed on a plank $P$. The firction between the upper surface of plank $P$ and the sphere is sufficient to prevent slipping. Friction between plank and ground is negligible. Initially plank $P$, is fixed to ground with help of a pin $N$. How will motion of sphere and plank be affected if, the pin $N$ is suddenly removed?
According to me the plank should move in opposite direction to that of sphere, since centre of mass must remain at rest.
But according to my teacher's explanation, the motion of plank and sphere will remain unaffected because since in question, it is given that that sphere is moving with constant speed, which means no acceleration. This implies there is no force acting hence, there would be no friction acting between plank and sphere. This explanation seems odd to me.
Please give appropriate explanation and point out any faults in any of the explanation mentioned above. Any suggestions are massively appreciated.