Calculating Depth & Distance (Edexcel GCSE Physics): Revision Note

A clap of thunder is heard 4 seconds after the corresponding flash of lightning. How far away is the thunderstorm? (The speed of sound in air is 330 m/s) 

Answer:

Step 1: List the known quantities

• Wave speed, v = 330 m/s

• Time, t = 4 s

Step 2: Write out the wave speed, distance and time formula 

Step 3: Re-arrange the equation to make distance (x) the subject

x = v × t

Step 4: Put known values into the equation

x = 330 × 4 = 1320 m

• So the distance to the thunderstorm is 1320 m

The sound wave released from a ship took 0.12 seconds to return. The speed of sound in water is 1500 m/s. What was the depth of the sea? 

Answer:

Step 1: List the known quantities

• Wave speed, v = 1500 m/s

• Time, t = 0.12 s

Step 2: Write out the wave speed, distance and time formula

Step 3: Rearrange the equation to make distance (x) the subject

x = v × t

Step 4: Put known values into the equation

x = 1500 × 0.12 = 180 m

Step 5: Half the distance to obtain the depth

d = 180 ÷ 2

Depth, d = 90 m

Don't forget to take into account if a sound wave has travelled twice the distance You can do this one of two ways:

• Halve the time at the beginning, or

• Halve the distance at the end