During the course of a demonstration the professor is called away. When he returns he finds a beaker of water that was at room temperature is now at a slightly higher temperature. There is a stirring rod on the desk and a cigarette lighter. The professor can assume that the temperature increase is due to either heat added or mechanical work done. mechanical work done on the system. heat added to the system.

Either heat added or mechanical work done.

Explanation:

Since he found stirring rod on the desk and a cigarette lighter. This means that the beaker was probably either heated with the aid of fire from the lighter.

Also, the stirring rod could have been used to stir the water which will increase the kinetic energy which also means an increase in temperature.

Thus, it's either heat was added or mechanical work was done as a result of stirring.

it takes about 30 days for it to break down

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me