Number of waves formed by a Bohr electron in one complete revolution in its third orbit is

The de Broglie wavelength of an electron in the third Bohr orbit of $H$-atom is

If the velocity of a hydrogen molecule is $5 \times 10^4 \, cm \, sec^{-1}$,then its de-Broglie wavelength is ............. $\mathring{A}$.

$A$ $200 \ g$ golf ball is moving with a speed of $5 \ m$ per hour. The associated wavelength is $(h = 6.625 \times 10^{-34} \ J \ s)$.

The velocity associated with a proton moving in a potential difference of $1000 \, V$ is $4.37 \times 10^{5} \, ms^{-1}$. If a hockey ball of mass $0.1 \, kg$ is moving with this velocity,calculate the wavelength associated with this velocity.

The ratio of de-Broglie wavelength of two particles $A$ and $B$ is $2: 1$. If the velocities of $A$ and $B$ are $0.05 \ ms^{-1}$ and $0.02 \ ms^{-1}$,respectively,then the ratio of their masses $m_A: m_B$ must be