A stone dropped from the top of a tower of height $300$ m splashes into the water of a pond near the base of the tower. When is the splash heard at the top?
(Given that the speed of sound in air is $340$ m/s and $g=9.8$ m/s²)
1. $7.7$
2. $8.7$
3. $6.7$
4. $7.8$

A steel wire has a length of $12.0$ m and a mass of $2.10$ kg. What should be the tension in the wire so that the speed of a transverse wave on the wire equals the speed of sound in dry air, at $20^{\circ}\text{C}$ (which is $343$ m/s)?
1. $4.3\times10^3$ N
2. $3.2\times10^4$ N
3. $2.06\times10^4$ N
4. $1.2\times10^4$ N

The speed of sound in air is:

A bat emits an ultrasonic sound of frequency $1000$ kHz in the air. If the sound meets a water surface, what is the wavelength of the reflected sound? (The speed of sound in air is $340$ m/sec and in water is $1486$ m/sec)
1. $3.4 \times 10^{-4}~\text{m}$
2. $1 . 49 \times 10^{- 3}  ~ \text{m}$
3. $2 . 34 \times 10^{- 2}   ~\text{m}$
4. $1 . 73 \times10^{- 3}   ~\text{m}$

A hospital uses an ultrasonic scanner to locate tumors in a tissue. What is the wavelength of sound in the tissue in which the speed of sound is $1.7~\text{km/s}$? The operating frequency of the scanner is $4.2~\text{MHz}$.