Why is helium used in inflating aeroplane tyres?

Why is Helium used in diving apparatus?

Why is red light used as a danger signal ?

Why does the air pressure in a car tyre increase during driving?

Why are shockers used in automobiles?

Why is the use of iodised salt advisable?

Why should the material used for making permanent magnet have high coercivity?

An aeroplane leaves an airport and flies due north at a speed of 1000 km per hour. At the same time another aeroplane leaves the same airport and flies due west at a speed of 1200 km per hour. How far apart will be the twö planes after 1(1/2) hours?.