Evan's Space

Wonders of Physics

N2005P1Q24 Sound – Reflection of sound from 2 walls


A man who is standing at a point X between two parallel walls (as shown in the diagram) fires a starting pistol.


He hears the first echo after 0.6s and another one after 0.8s. How long after firing the pistol will he hear the next echo?


View video tutorial to visualise the distance travelled.

Time taken to hear next echo = 0.6 + 0.8 = 1.4s

The distance travelled by sound (left and right) from X is the same during 3rd and 4th echos.

Hence 3rd and 4th echos actually coincide. And time taken is 0.6 + 0.8 = 1.4s.


2 thoughts on “N2005P1Q24 Sound – Reflection of sound from 2 walls

  1. May I know if the experiment is about 2 person standing a certain length apart and one person fires a pistol and the other person start the stop-watch when he sees the flash. What is the assumption made? Thank you.

    • The experiment u mentioned is usually used to measure speed of sound. Let the distance between the 2 persons be d. If person A fires gun, person B starts timing when he sees the flash/smoke. B stops timing when he hears the sound. Let time be t1. Repeat experiement let it be t2. Either swop position or roles (to cancel effect of prevailing wind), get t3 and t4. Find average time. Speed = d/average time. Assumption is light travel almost instantly and that wind blows at constant speed and direction. Hope it helps.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s