CBSE Class 9 Answered

(a) Speed of sound, v = 5960 m/s 

time taken to reflect, t = 0.02 s 

Distance = (speed x time/2) 

distance = 5960 x 0.02/ 2 = 59.2 m ≈ 59 m 

Thus, the block is 59 m away from the transmitter. 

(b) Application of ultrasound in medical field: 

Medical application

(1) Ultrasound Imaging:- Ultrasounds are used to get images of muscles, blood vessels and organs of human body.

(2) therapeutic applications:- a non-invasive therapy for musculoskeletal disorders and cancer treatment. 

(c) Two practical applications of reflection of sound waves: 

(i) Hearing aid: It is a device used by people who are hard of hearing. Here the sound waves, which are received by the hearing aid are reflected into a narrower area leading to the ear.

(ii) Soundboards: Curved surfaces can reflect sound waves. This reflection of sound waves is used in the auditorium to spread the waves uniformly throughout the hall. Reflection of sound waves is done by using Sound Boards. The speaker is located at the focus of the soundboard.