Sound travels in a mixture of two moles of helium and n moles of hydrogen. If rms speed of gas molecules in the mixture is $$\sqrt2$$ times the speed of sound, then the value of n will be :

An object is taken to a height above the surface of earth at a distance $${5 \over 4}$$ R from the centre of the earth. Where radius of earth, R = 6400 km. The percentage decrease in the weight of the object will be :

A bag of sand of mass 9.8 kg is suspended by a rope. A bullet of 200 g travelling with speed 10 ms^$$-$$1 gets embedded in it, then loss of kinetic energy will be :

A ball is projected from the ground with a speed 15 ms^$$-$$1 at an angle $$\theta$$ with horizontal so that its range and maximum height are equal,
then 'tan $$\theta$$' will be equal to :