Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Which Bottle get Emptied First?


To analyse and compare which bottle get emptied first.


If a hole is made in a water bottle with its cap open, water goes out through the hole. The speed at which water goes out depend on the height of the open water surface above the hole. This is based on well known Bernoulli's principle. In this experiment, a situation is created which needs a careful analysis before applying this principle.


two one litre bottles, two straws of unequal length


Take two bottles in which a hole is made in the bottom and a straw is fixed in the cap. The straws in the two bottles are of unequal lengths. Fill the bottle with water. You will have to close the bottom hole with your finger. Screw the cap tightly in each bottle.


Now invert the two bottles simultaneously and remove fingers to open the holes. Water will start falling down through the straws. Which bottle get emptied first? Why?


You must carefully think of the height between the point of release of water and the free surface. Then use the Bernoulli's principle and explain the observation.