The total energy of an electron in the second excited state of hydrogen atom is about $$-1.51 \mathrm{~eV}$$. Its kinetic energy in this state is
The masses of block $$A$$ and $$B$$ are $$m$$ and $$M$$, respectively. Between $$A$$ and $$B$$, there is a constant frictional force $$F$$ and $$B$$ can slide on a smooth horizontal surface. A is set in motion with velocity $$3 v_0$$ while $$B$$ is at rest. What is the distance moved by $$A$$ relative to $$B$$ before they move with the same velocity?
Magnetic moment of bar magnet is $$2 M$$. The work done to turn the magnet by $$90^{\circ}$$ of magnet in direction of magnetic field $$B / 2$$ will be
The wavelength of two waves are 40 and $$42 \mathrm{~cm}$$ respectively. If the temperature of the room is $$20^{\circ} \mathrm{C}$$ then what will be the number of beats produced per second by these waves. When the speed of sound at $$0^{\circ} \mathrm{C}$$ is $$332 \mathrm{~m} / \mathrm{s}$$ ?