When an object travels at a speed higher than that of sound in air, it produces shock waves. These shock waves carry a large amount of energy. The air pressure variations associated with this type of shock waves produce a very sharp and loud sound called sonic boom or supersonic speed.

No, sound cannot travel through vacuum.
Because, sound can travel only when there are particles, which can be compressed and rarefied in the medium.

Tuning fork

1. Musical instruments such as shehnai, trumpets and Nathaswaram, Megaphones, loudspeakers use the property of reflection of sound to guide most of the sound waves from the source in the forward direction towards the audience.
2. In stethoscopes, sound produced in the body reaches doctor's ears by multiple reflection of sound that happen in the connecting tube.
3. Echo is used to find the distance between two distant objects.
4. Ultrasound is used in examining inner parts of the body and also in marine surveying.
5. Ultrasound is used in cleaning technology, to detect cracks and flaws to form the image of the heart through 'echocardiography'.
6. Ultrasound is employed to break stones formed in the kidney.
7. 'SONAR' is a device that uses ultrasonic waves to measure the distance, direction and speed of the underwater objects.
8. In Electrocardiogram (ECG) the sound variation produced by the heart is converted into electrical signals, which represents the electrical activity of the heart muscle.

Velocity of sound = 340 ms^-1
Height of tower = 750 m
Total distance travelled = 2 x 750 = 1500 m
\(Valocity=\frac {distance}{time}\) 
\(340=\frac {1500}{time}\) 
\(time=\frac {1500}{340}=4.4s\)
After 4.4 s, the splash is heard.