Resonance is produced between a turning fork and a resonance column tube with upper end open and lower end closed by water surface. If the frequency of the tuning fork is 800 Hz , and first two resonances are observed at lengths $9.75 \mathrm{~cm}, 31.25 \mathrm{~cm}$,
Find the length at which the third resonance occurs? Also find the speed of sound.
52.75 cm and $344 \mathrm{~ms}^{-1}$
31.25 and $330 \mathrm{~ms}^{-1}$
62.60 cm and $335 \mathrm{~ms}^{-1}$
43.10 cm and $340 \mathrm{~ms}^{-1}$
A boy, standing at a certain height, kicks a football horizontally with a velocity of $19.6 \mathrm{~ms}^{-1}$. What will be the ratio of horizontal and vertical components of velocities after $2 s$ ?
$1: \sqrt{2}$
$\left(\frac{\sqrt{3}}{2}\right): 1$
$1: 1$
$ 1:0.5$
A capacitor of capacitance $8 \mu \mathrm{~F}$ is fully charged by connecting it to a source of 200 V . It is then disconnected from the supply and connected to an uncharged capacitor of capacitance $4 \mu \mathrm{~F}$. The electrostatic energy lost in this sharing is:
$21.34 \times 10^{-2} J$
$5.33 \times 10^{-2} J$
$3.53 \times 10^{-3} J$
$10.67 \times 10^{-2} J$
A hydrogen atom absorbs energy and rises to $n=3$ state from its ground state $n=1$. If the potential energy of the atom at its ground state is -13.6 eV , find the wave length emitted by it when it returns to its ground state:
{Planck's constant $=6.6 \times 10^{34} \mathrm{~J} \mathrm{~s}$ }
$12000^{\circ} \mathrm{A}$
$1020^{\circ} \mathrm{A}$
$7000^{\circ} \mathrm{A}$
$4000^{\circ} \mathrm{A}$
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