686

The image shows a page from a book, likely containing a series of physics or chemistry problems. Here’s a transcription of some of the problem numbers and key details mentioned: - **686**: The problem involves determining the force acting on a specific area of a piston exposed to external pressure. - **687**: This problem is about finding the temperature of a gas under certain conditions. - **688**: The problem mentions calculating the density of a liquid given in a vessel with specific parameters. - **689**: The task is to find the pressure exerted by a column of liquid with a given height and density. - **690**: This involves measuring how much water evaporates under certain conditions in a given timeframe. Each problem likely requires applying principles of physics or chemistry related to pressure, density, temperature, and evaporation.