Figure 6 shows a large tank of water - Edexcel - GCSE Physics Combined Science - Question 4 - 2020 - Paper 1

To calculate the wavelength, we need to divide the distance between points L and M by the number of wavelengths present.

1. Number of wavelengths = 10 (observed visually in the figure)
2. Wavelength = Distance / Number of wavelengths = $\frac{32 m}{10} = 3.2 m$.

Frequency can be calculated using the formula:

$f = \frac{n}{t}$

where $n$ is the number of peaks (12) and $t$ is the time (15 s).

Substituting the values: $f = \frac{12}{15} = 0.8 Hz$.

Arrows should be drawn to indicate the movement of the rock at R, which will be parallel to the direction of the seismic wave. The arrows should point in the direction the rock moves as the wave compresses and stretches it.

Using the equation:

$\text{wavelength} = \frac{\text{wave speed}}{\text{frequency}}$

we substitute the values: wave speed = 7 km/s = 7000 m/s and frequency = 12 Hz.

Therefore: $\text{wavelength} = \frac{7000 m/s}{12 Hz} = 583.33 m$.

Rounding gives approximately 580 m.

Counting the waves of a seismic wave arriving is not suitable because:

1. Seismic waves travel underground and their arrival cannot be visually counted like surface waves.
2. The technician might not accurately count waves as they can happen too quickly or be too faint, leading to a risk of missing waves or losing count.