Figure 11 shows a large tank of water - Edexcel - GCSE Physics - Question 6 - 2020 - Paper 1

The wavelength can be calculated using the formula:

$\text{Wavelength} = \frac{\text{Distance between L and M}}{\text{Number of wavelengths}}$

Given that the distance is 32 m, and assuming there is one wavelength per distance:

Wavelength = 32 m / 10 = 3.2 m

To find frequency, use the formula:

$\text{Frequency} = \frac{\text{Number of peaks}}{\text{Time}}$

Substituting the values:

Frequency = 12 / 15 = 0.8 Hz.

Arrows should be drawn to indicate that the rock at R moves in the direction of the seismic wave, which is a longitudinal wave. This means the arrows will show back-and-forth motion along the path of the wave.

Using the formula:

$\text{Wavelength} = \frac{\text{Wave Speed}}{\text{Frequency}}$

Substituting the values:

Wave Speed = 7 km/s = 7000 m/s,

Frequency = 12 Hz,

Wavelength = 7000 m/s / 12 Hz = 583.33 m (or approximately 580 m if rounding).

This method is not suitable because seismic waves cannot be easily counted like water waves. Seismic waves arrive as a series of peaks that may be difficult to distinguish, and relying on counting during a short time frame may not provide an accurate measurement. Additionally, because seismic waves travel through solid materials, their detection may require specialized equipment beyond simple counting.