RI 2024 H2 Physics Promo Sect C QP

Name: ( ) CT Group: 25S0 RAFFLES INSTITUTION 2024 YEAR 5 PROMOTION EXAMINATION H2 PHYSICS 9749 2 h 30 min Section C RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFL ES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFL ES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFL ES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFL ES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFLES INSTITUTION RAFFL ES INSTITUTION Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Name, Index Number and CT Group in the spaces at the top of this page. Write in dark blue or black pen on both sides of the paper. You may use a 2B pencil for any diagrams or graphs. The use of an approved scientific calculator is expected, where appropriate. Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 21 / 17 22 / 19 Deductions There are 11 printed pages, inclusive of the cover page, in this booklet.

2 © Raffles Institution 21 Read the passage below and answer the questions that follow. An earthquake is the shaking of the Earth's surface resulting from a sudden release of energy in the outermost rocky shell of Earth that creates seismic waves. Earthquakes can range in intensity, from those so weak they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. Earth is made up of several layers, namely, the core, mantle and crust as shown in Fig. 21.1. Fig. 21.1 (not to scale) The core is made of two layers , i.e., the inner core and the outer core. The inner core at the centre of Earth is a hot, dense ball of solid iron. The outer core which is sandwiched between the inner core and the mantle is composed of liquid iron and nickel. The mantle is the largest and thickest layer of Earth, making up 84% of the planet's total volume and its structure is mostly silicate. The outermost layer known as the crust is thin and rigid. The crust is mostly made up of rocks. Earthquakes occur in the mantle or crust. They can occur naturally or be induced by human activities, such as mining, fracking (hydraulic fracturing) and nuclear tests. The initial point of rupture is called the hypocentre or focus while the ground level directly above it is the epicentre. Earthquakes are primarily caused by geological faults but also by volcanic activity, landslides, and other seismic events. Every earthquake produces different types of seismic waves, which travel through rock with different velocities, i.e., the longitudinal P-waves (also known as shock or pressure waves), the transverse S- waves ( shear waves) and surface waves ( also known as Rayleigh and Love waves). Propagation velocity of the seismic waves varies depending on the density and elasticity of the medium. In the Earth's interior, the P -waves travel much faster than the S - waves. The differences in travel time from the epicentre to the observatory are a measure of the distance and can be used to image both sources of earthquakes and structures within the Earth. The depth of the hypocentre can also be computed roughly. 5100 km mantle core inner core outer core mantle crust liquid solid 2900 km 6378 km crust

3 © Raffles Institution [Turn over (a) Distinguish between a longitudinal wave and a transverse wave. [2] (b) A large earthquake occurs very near the surface of the Earth at a particular location and both seismic P- waves and S- waves are produced. The P -waves and S- waves travel through the Earth away from the epicentre of the earthquake. The average speed of the P-waves is 7.98 km s–1 and the average speed of the S-waves is 4.75 km s –1. A seismograph which measures and records the vibrations of the earthquake detects the arrival of the S -waves 2 minutes 50 seconds after the arrival of the P-waves. (i) Calculate the time taken for the S -waves to travel from the epicentre of the earthquake to the seismograph. time taken = s [2] (ii) Determine the distance of the epicentre of the earthquake from the seismograph. distance = km [1]

4 © Raffles Institution (c) Fig. 21.2 shows an epicentre at point A and a seismograph at point B which is located on the opposite side of the Earth. Fig. 21.2 Explain why the seismograph can detect the P -waves but not the S -waves produced by the earthquake. [1] A B

5 © Raffles Institution [Turn over (d) Peak Ground Acceleration (PGA) is the maximum acceleration of the ground during an earthquake. To gauge the potential damage of earthquakes, the United States Geological Survey measures PGA to create an intensity scale for the effects of earthquakes. This scale is shown in Table 21.1. Table 21.1 intensity scale PGA / m s−2 maximum ground velocity / m s−1 perceived shaking potential damage I < 0.017 < 0.001 not felt none II−III 0.017 – 0.14 0.001 – 0.011 weak none IV 0.14 – 0.38 0.011 – 0.034 light none V 0.38 – 0.90 0.034 – 0.081 moderate very light VI 0.90 – 1.8 0.081 – 0.16 strong light VII 1.8 – 3.3 0.16 – 0.31 very strong moderate VIII 3.3 – 6.4 0.31 – 0.60 severe moderate to heavy IX 6.4 – 12.2 0.60 – 1.16 violent heavy X+ > 12.2 > 1.16 extreme very heavy (i) Assuming that the ground movements can be modelled as simple harmonic oscillations, calculate the frequency and the amplitude of the strongest earthquake within the intensity scale of V. frequency = Hz amplitude = m [3]

6 © Raffles Institution (ii) Earthquakes can cause the ground to accelerate in three perpendicular directions, x, y and z, as shown in Fig. 21.3. Fig. 21.3 During a particular earthquake, the maximum ground accelerations along x, y and z are: ax = 8.0 m s–2, ay = az = 1.5 m s–2 Show that the maximum possible resultant ground acceleration that could be produced by these vibrations is 8.3 m s–2. [2] (iii) Explain why, in reality, the maximum resultant ground acceleration might be less than 8.3 m s–2. [1] x y z

7 © Raffles Institution [Turn over (e) It is suggested that the Peak Ground Acceleration (PGA) decreases with distance r from the epicentre according to the equation: PGA k r= where k is a constant. Table 21.2 shows some data from an earthquake. Table 21.2 distance r from epicentre / km 56 84 120 220 PGA / m s–2 0.71 0.60 0.50 0.32 Use the data in Table 21.2 to explain whether the suggested equation is valid. [2] (f) During an earthquake, the amplitude of a particular building’s oscillation is observed to be much larger than the amplitude of the movements of the ground. (i) State the name of this phenomenon. [1] (ii) State two properties of the building that will affect how strongl