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

To calculate the time taken by the P-wave, we use the formula:

ext{time} = rac{ ext{distance}}{ ext{speed}}

Inserting the values:

ext{time} = rac{5800 ext{ km}}{12000 ext{ m/s}} = rac{5800 imes 1000 ext{ m}}{12000 ext{ m/s}} = rac{5800000}{12000} ext{ s} \ ext{time} = 483.33 ext{ s}

The amplitude of seismic waves generally decreases as the distance from the earthquake source increases. For the two earthquakes represented in the graph:

• Earthquake Strength 5: The amplitude drops more gradually compared to strength 3, indicating that stronger earthquakes produce higher initial amplitudes that decrease over distance.

• Earthquake Strength 3: This earthquake shows a steeper decline in amplitude with distance, suggesting that it dissipates energy more quickly than the stronger earthquake.

Sonar operates by emitting sound pulses underwater. The process can be explained as follows:

1. Sonar Pulse Emission: A submarine emits a sonar pulse, which travels through the water at the speed of sound, approximately 1500 m/s.

2. Reflection of Signal: The pulse travels until it encounters another submarine, where it is reflected back to the original submarine.

3. Detection and Timing: The time taken for the pulse to return is measured. Using the formula:

$$ext{distance} = ext{speed} imes ext{time}$$

4. Calculating Distance: Since the pulse has to travel to the second submarine and back, the total distance covered is twice the distance to the second submarine. Hence, the distance to the second submarine is:

ext{Distance to submarine} = rac{ ext{speed} imes ext{time}}{2}