Sound Questions

A sound absorber attenuates the sound level by $20\text{dB}$. The intensity decreases by a factor of:

When two tuning forks (fork $1$ and fork $2$) are sounded simultaneously, $4$ beats per second are heard. Now, some tape is attached on the prong of the fork $2$. When the tuning forks are sounded again, $6$ beats per second are heard. If the frequency of fork $1$ is $200\text{ Hz}$, then what was the original frequency of fork $2$?

A motor cycle starts from rest and accelerates along a straight path at $2{\text{m/s}}^2$. At the starting point of the motor cycle there is a stationary electric siren. How far has the motor cycle gone when the driver hears the frequency of the siren at $94\%$ of its value when the motor cycle was at rest? (speed of sound $=330{\text{m s}}^{-1}$).

A cylindrical tube, open at both ends, has a fundamental frequency, $f$, in air. The tube is dipped vertically in water so that half of it is in water. The fundamental frequency of the air-column is now: