General Wave Properties: Question 5
Syllabus 3.1
At an adventure park, a taut steel zip-line cable stretches between two towers. A gust of wind makes one end of the cable flick briefly up and down, sending a wave pulse travelling horizontally along the cable towards the far tower. Separately, a cyclist uses a hand pump to inflate a tyre: each stroke of the pump forces a pulse of compressed air along the flexible connecting hose, alternating with pulses of less compressed air, until the pulses reach the tyre valve. Which row correctly identifies the type of each wave?
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Worked solution
Step 1: Classify the wave on the zip-line cable
The wind flicks the cable up and down, while the wave pulse itself travels horizontally along the cable towards the far tower. The vibration of the cable is perpendicular to the direction the wave travels, so this is a transverse wave.
Step 2: Classify the wave in the pump hose
Each pump stroke sends a pulse of compressed air along the hose, alternating with pulses of less compressed air, and these pulses travel along the length of the hose towards the valve. The air is alternately compressed and expanded along the same direction that the wave travels, so this is a longitudinal wave.
Step 3: Match to the correct option
- Zip-line cable: transverse
- Pump hose: longitudinal
This matches option C.
Why the other options are wrong
| Option | Claim | Error |
|---|---|---|
| A | Cable longitudinal, hose transverse | Both classifications are swapped compared with the correct answer |
| B | Both transverse | The pump hose carries compressions along its length, not a sideways vibration, so it cannot be transverse |
| D | Both longitudinal | The cable vibrates up and down, perpendicular to its length, so it cannot be longitudinal |
Final answers
- Zip-line cable transverse; pump hose longitudinal, option C