A lead bullet moving with velocity ' $v$ ' strikes a wall and stops. If $50 \%$ of its energy is converted into heat, then the increase in temperature is ( $s=$ specific heat of lead)

A pendulum is oscillating with frequency ' $n$ ' on the surface of earth. If it is taken to a depth $\frac{R}{4}$ below the surface of earth, new frequency of oscillation of depth $\frac{\mathrm{R}}{4}$ is ( $\mathrm{R}=$ radius of earth)

The ratio of minimum wavelengths of Lyman and Balmer series will be

If a $10 \mu \mathrm{C}$ charge exists at the centre of a square, the work done in moving a $2 \mu \mathrm{C}$ point charge from corner A to corner B of a square ABCD is