A simple pendulum completes $420$ oscillation in $2 \mathrm{minutes}$. Calculate the time period and frequency.

A person standing on a ground hears a thunder $4 \mathrm{s}$ after seeing a flash of lightning. How high is the cloud from the ground?
($\mathrm{speed} \mathrm{of} \mathrm{sound} \mathrm{in} \mathrm{air}=343 \raisebox{1ex}{$\mathrm{m}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{s}$}\right.$)

The deepest part of the oceans in the world is Mariana Trench in the Pacific Ocean. It is $11,000 \mathrm{m}$ deep. How long will it take for sound transmitted by a ship, from the surface of the water above the trench to be reflected? ($\mathrm{speed} \mathrm{of} \mathrm{sound} \mathrm{in} \mathrm{sea} \mathrm{water}=1500 \raisebox{1ex}{$\mathrm{m}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{s}$}\right.$)