A student and her friend obtain an approximate value for the speed of sound in air by using echoes.
She positions herself a long way from a wall that reflects sound.
She claps at a steady rate.
She then alters her clapping rate until each clap matches the echo from the previous clap.
Her friend uses a stopwatch to find the time $t$ between claps.
They measure how far the wall is away.
The time $t$ between claps is measured four times.
The values of $t$, in seconds, are listed below.
$0.87 \quad 0.97 \quad 0.94 \quad 0.88$
(a(i))[2]
Calculate $t_{av}$, the mean value of $t$. Give your answer to 2 decimal places.
$t_{av}$ = [BLANK] s
(a(ii))[1]
Suggest why it is reasonable to quote $t_{av}$ to 2 decimal places.
(b(i))[1]
A metre rule is not a suitable instrument for finding this distance.
Suggest a device that can be used to measure this distance.
(b(ii))[1]
The speed $v$ of sound in air is defined by
$v = \frac{2s}{t_{av}}$.
Calculate $v$.
$v$ = [BLANK] m s$^{-1}$
(b(iii))[1]
Suggest one reason why the speed of sound in air measured by this method is only approximate.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Average time = 0.915 s” …