Question

A thermos bottle containing coffee is vigorously shaken. If coffee is considered as a system, then the temperature of coffee will

• A. Increases slightly
• B. fall
• C. remain the same
• D. can't be determined

Answer 1

The correct option is A Increases slightly

As thermos flask is insulated, so no heat energy added to the system, $△Q=0$

Work is done on the system by shaking it against viscous force. Hence $△w=-ve$

Internal energy $=△U=△Q-△w=0-(-△w)\Rightarrow △U=+△w$

$△U=+ve$

So, the temperature of the system will increase due to increase in internal energy.