There are ten tubewells In a lane of fifty houses. What could be the long term impact on the water table?

What should be the order of magnitude of the minimum fequency of electromagnetic waves that could be used to detect the presence of an aircraft 50 m long and

What helps the diving mammals to stay under water for a long time?

What should be the order of magnitude of the minimum fequency of electromagnetic waves that could be used to detect the presence of a bird 0.1m long? From what sources of electromagnetic radiation would you be able to generate radiation of these wavelengths?

Agreat physicist of this century (RA.M. Dirac) loved playing with numerical values of Fundamental constants of nature. This led him to an interesting observation. Dirac found that from the basic constants of atomic physics (c, e, mass of electron, mass of proton) and the gravitational constant G, he could arrive at a number with the dimension of time. Further, it was a very large number, its magnitude being close to the present estimate on the age of the universe (~15 billion years) . From the table of fundamental constants in this book, try to see if you too can construct this number (or any other interesting number you can think of). If its coincidence with the age of the universe were significant, what would this imply for the constancy of fundamental constants ?

A glass plate of length 10 cm, breadth 4 cm and thickness 0.4 cm weighs 40 g in air. If it is held vertically with long side horizontal and the plate half immersed in water, what will be its apparent weight? Surface tension of water = 70 dyne cm^-1 .

500 persons took dip in a rectangular tank which is 80 m long and 50 m broad. What is the rise in the level of water in the tank. If the average displacement of water by a person is 0.04 m^3 ?