When a hot metal cylinder is dropped into a sample of water, the water molecules to reach the final temperature.

When a hot metal cylinder is dropped into a sample of water, the water molecules will move with greater speed to reach the final temperature.

Explanation:

As we know that internal energy of the system of gas or any fluid or any matter is only function of its temperature.

Which means if the internal energy of the system is increased then its temperature must have to increase which means the kinetic energy of the molecules of that system will have to increase

So in the given case if hot cylinder is dropped in water then due to energy exchange between cylinder and water the temperature of water will increase and due to this the molecules of water will have more internal energy.

Due to increase in internal energy of molecules of water the kinetic energy of the molecules will increase and this leads to speed up of the water molecules.

if the thermos has a vacuum innner, then heat through conv currents and conduction are reduced = vacuum flask