Final answer:
The marble oscillates in the bowl due to the net force directed toward the bowl's bottom, creating a restoring force that ensures simple harmonic motion until dissipative forces bring it to rest.
Step-by-step explanation:
The marble undergoes oscillatory motion when released from a position about halfway from the top of a semi-spherical bowl because the net force exerted on the marble always has a component directed toward the bottom of the bowl (option b). This force is known as the restoring force which is directed towards the stable equilibrium point at the bottom of the bowl. As the marble rolls up the side of the bowl, gravity acts to slow it down until it stops and rolls back towards the center, creating oscillatory motion or simple harmonic motion (SHM). This oscillatory motion continues, with the marble rising to increasingly lower heights on either side of the bowl due to dissipative forces such as friction, which gradually decrease the amplitude of the oscillation until the marble comes to rest at the equilibrium point at the bottom of the bowl.