5 (a) Earthquakes produce seismic waves and infrasound waves - Edexcel - GCSE Physics - Question 5 - 2018 - Paper 1

To calculate the time taken for the P-wave to travel a distance of 5800 km at a speed of 12000 m/s, we can use the formula:

$$t = \frac{d}{v}$$

where:

• $t$ is the time,
• $d$ is the distance (5800 km = 5800000 m),
• $v$ is the speed (12000 m/s).

Calculating gives:

$$t = \frac{5800000 \text{ m}}{12000 \text{ m/s}} \approx 483.33 \text{ s}$$

Thus, the time of travel = 483.33 s.

From the graph, it can be observed that:

• For earthquake strength 3, the amplitude decreases steadily as the distance increases.
• For earthquake strength 5, the amplitude also decreases but at a slower rate compared to strength 3. This indicates that stronger earthquakes maintain higher amplitudes over greater distances compared to weaker ones.

Sonar operates by emitting sound waves through water and detecting the echo that reflects back from an object, such as another submarine. The process is as follows:

1. The first submarine emits a sonar pulse, which travels at the speed of sound in water (approximately 1500 m/s).
2. The pulse travels through the water until it encounters the second submarine, where it reflects back.
3. The first submarine measures the time taken for the echo to return.
4. Knowing the speed of sound and the time taken, the distance to the second submarine can be calculated using the formula:

$$d = v \times t$$

However, since the signal travels to the second submarine and back, the distance to the submarine is half the total distance calculated. Therefore, the formula for calculating the one-way distance becomes:

$$d = \frac{v \times t}{2}$$

5. This method allows submarines to navigate and locate each other under the water effectively.