In which of the following cases , the net force is zero?

I) A ball freely falling from a certain height

II) A cork floating on the surface of water

III) An object floating in air

The velocity of a particle at highest point of the vertical circle is $\sqrt{3rg}$. The tension at the lowest point, if mass of the particle is $m$, is

একটি চাকার জড়তার ভ্রামক $5 k g{m}^{2}$ চাকাটিতে $10^{5}$   ঘুর্ণন গতিশক্তিতে ঘুরতে কত কৌনিক বেগের প্রয়োজন হবে ? 

The breaking strength of a string is 55 kg wt. The maximum permissible speed of a stone of mass 5 kg which revolved in a vertical circle of radius 4 m with the help of is the string is g=10 ${s}^{2}$.

The momentum of a body of given mass is proportional to its: