Sound Waves
4 marks · NormalA student investigates the speed of sound in air using the echo method. She stands 120 m from a large wall. She claps her hands and starts a stopwatch when she sees the clap, stopping the watch when she hears the first echo. The time recorded is 0.7 seconds.
Calculate the distance travelled by the sound wave from the student to the wall and back.
Calculate the speed of sound in air in this experiment. Give your answer to 2 significant figures. Use the equation:
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 240 m
(b) 340 m/s
Common mistakes: Using only 120 m instead of 240 m for distance; Not using 2 significant figures
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Distance is 120 x 2 = 240 m.
M1 (b) · 1 mark · Uses speed = distance/time formula.
M1 (b) · 1 mark · Correct substitution of values: 240 m / 0.7 s.
A1 (b) · 1 mark · Correct answer (approx 340 m/s) to 2 significant figures, correct unit. (follow-through)
Worked solution
a) The sound travels from the student to the wall and back, so total distance = 120 m x 2 = 240 m.
b) Speed = distance / time = 240 m / 0.7 s = 342.857... m/s = 340 m/s (2 significant figures).