Question 6: When a sealed thermo flask bottle full of hot coffee is shaken, what are the changes, if any, in;
(a) the temperature of the coffee
(b) the internal energy of the coffee?

ANSWER

When the thermo flask bottle with hot coffee in it is shaken heavily, work is done on it. This work done increases the kinetic energy of the molecules of coffee. As such kinetic energy is proportional to the temperature of the body, therefore, the temperature of the coffee increases.
The flask is an insulated bottle so no heat can go out of it. Therefore, the work done will also increase the internal energy of the contents (coffee).