Question

Difficulty: MediumProduction, Propagation, and Classification of Waves

A water wave moving horizontally across the surface of a pond causes a floating cork to move vertically up and down. The cork completes one full oscillation every 0.50 s0.50\text{ s}, and the horizontal distance between two consecutive wave crests is 1.2 m1.2\text{ m}. What is the speed of propagation of the wave, and how is the wave classified?

  1. 2.4 m s12.4\text{ m s}^{-1}, transverse mechanical waveAnswer
  2. B
    2.4 m s12.4\text{ m s}^{-1}, longitudinal mechanical wave
  3. C
    0.60 m s10.60\text{ m s}^{-1}, transverse mechanical wave
  4. D
    2.4 m s12.4\text{ m s}^{-1}, transverse electromagnetic wave

Answer

2.4 m s12.4\text{ m s}^{-1}, transverse mechanical wave
The frequency of oscillation is f=1T=10.50 s=2.0 Hzf = \frac{1}{T} = \frac{1}{0.50\text{ s}} = 2.0\text{ Hz}. Using the wave formula v=fλv = f\lambda, the propagation speed is v=2.0 Hz×1.2 m=2.4 m s1v = 2.0\text{ Hz} \times 1.2\text{ m} = 2.4\text{ m s}^{-1}. Because the cork vibrates vertically while the wave propagates horizontally, the oscillations are perpendicular to the propagation direction, defining a transverse wave. Since water is required for propagation, it is a mechanical wave.

Step-by-Step Solution

1
Determine the frequency of the wave from the period.
The period T=0.50 sT = 0.50\text{ s}, so frequency f=1T=10.50=2.0 Hzf = \frac{1}{T} = \frac{1}{0.50} = 2.0\text{ Hz}.
Frequency is the reciprocal of the time period of oscillation.
2
Calculate the wave speed using the wave equation.
v=fλ=2.0 Hz×1.2 m=2.4 m s1v = f \lambda = 2.0\text{ Hz} \times 1.2\text{ m} = 2.4\text{ m s}^{-1}.
Wave speed equals the product of frequency and wavelength.
3
Classify the wave based on particle motion and medium requirement.
Particle displacement is perpendicular to wave direction (transverse) and requires water as a medium (mechanical).
Perpendicular oscillation defines transverse waves, and medium dependence defines mechanical waves.

Key Concept

Wave speed calculation and wave classification based on vibration direction and medium requirements.
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