Answer:
Explanation:The rotational inertia of any object depends directly on the distance the mass is from the axis of a rotating object
Having more mass at the sides will increase the rotational inertia of the object that is why a Hollow sphere having same M and R as the solid one has more rotational inertia as it has more mass at the sides.
The sphere have some mass at the center but most of its mass is closer to its radius and thus have more inertia than flat Disk.
The same relation exist between a flat disk and hollow sphere. The hollow sphere have some mass at the center but most of its mass is closer to its radius and thus have more inertia.
The rotational of the objects can be calculated by these equations

Answer:
This is because below 4°c, water unlike other materials becomes less dense when it's temperature is further lowered.
Explanation:
Due to the unusual nature of water; at about 4°c, the behavior of the density of water in relation to its temperature reverses. This means that water becomes less dense as it becomes colder below 4°c. The colder parts therefore floats to the top of the water body while the warmer part sinks allowing the top to freeze and the remaining body below to remain in its liquid state.
The freezing of the top of the lake alone protects the remaining depth of water from freezing by acting as an insulator and preventing further heat loss from the water to the ambient space. If this had not been the case, and water froze all through, marine lives will freeze to death and it will be more difficult to melt the ice come the next summer.
This behavior is due to the hydrogen bonding of the water molecules.
It will not explode since the mass of the cotton balls is so low but rather will most likely break the lock and hinges and come out.