Properties of wavesIB MYP Sciences: Subtopic test

1. 1
   A buoy floats on the sea off the coast of Portugal. As waves pass, the buoy bobs up and down but stays in almost the same place. An oceanographer counts 12 wave crests passing the buoy in 60 seconds.

   (a)

   Which statement about the energy carried by the waves is correct?

   [1 mark]

   • AThe wave transfers energy through the water, but the water itself does not travel along with the wave
   • BThe wave carries water from the open sea to the coast
   • CThe wave uses up its energy to push the buoy along the surface
   • DThe wave transfers matter but no energy

   (b)

   The buoy moves up and down while the wave travels horizontally across the surface. What type of wave is this?

   [1 mark]

   • ALongitudinal, because the vibrations are parallel to the direction of travel
   • BTransverse, because the vibrations are at right angles to the direction of travel
   • CLongitudinal, because the wave carries energy
   • DTransverse, because the wave has a high frequency

   (c)

   Calculate the frequency of the waves and state their period.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in Nairobi uses a dipper that vibrates 8 times every second to make ripples in a shallow water tank. The ripples have a wavelength of 3.0 cm.

   (a)

   What is the frequency of the ripples?

   [1 mark]

   • A3 Hz
   • B24 Hz
   • C8 Hz
   • D0.125 s

   (b)

   Which distance is equal to one wavelength of the ripples?

   [1 mark]

   • AFrom a crest to the next trough
   • BFrom the dipper to the wall of the tank
   • CThe height of a crest above the undisturbed water level
   • DFrom one crest to the next crest

   (c)

   Calculate the speed of the ripples. Give the unit.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Students in Singapore investigate how the depth of water affects the speed of waves. In a long, shallow channel they make a single wave at one end and use a stopwatch to time how long it takes to travel 2.0 m to the far end. Each depth is tested three times. At a depth of 2 cm the times are 4.6 s, 4.4 s and 4.5 s. At a depth of 4 cm the times are 3.3 s, 3.1 s and 3.2 s.

   (a)

   State the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   Calculate the mean speed of the waves at each depth and describe the trend in the results.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   After a major tsunami in the Indian Ocean, many countries built warning systems. Deep-sea sensors detect the wave as it passes, and sirens and phone alerts warn people on the coast. A tsunami crosses the open ocean at about 200 m/s with a wavelength of about 100 km. The warning systems cost millions to build and maintain, and some false alarms have led to costly evacuations.

   (a)

   Calculate (i) the frequency of the tsunami wave, and (ii) the time in hours that the wave takes to reach a coast 2400 km from the earthquake.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of spending public money on tsunami warning systems, and evaluate whether governments should do so.

   [6 marks]

   Total for question 4: 12 marks

End of questions