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NEET PHYSICSWAVEMedium

Question

A wave in a string has an amplitude of 2 cm2 \text{ cm}. The wave travels in the +ve direction of x-axis with a speed of 128 ms1128 \text{ ms}^{-1} and it is noted that 55 complete waves fit in 4 m4 \text{ m} length of the string. The equation describing the wave is:

A

y=(0.02) msin(7.85x+1005t)y=(0.02)\text{ m} \sin(7.85x+1005t)

B

y=(0.02) msin(15.7x2010t)y=(0.02)\text{ m} \sin(15.7x-2010t)

C

y=(0.02) msin(15.7x+2010t)y=(0.02)\text{ m} \sin(15.7x+2010t)

D

y=(0.02) msin(7.85x1005t)y=(0.02)\text{ m} \sin(7.85x-1005t)

Step-by-Step Solution

  1. Determine the Amplitude (AA): The amplitude is given as 2 cm=0.02 m2 \text{ cm} = 0.02 \text{ m}.
  2. Calculate the Wavelength (λ\lambda): It is given that 55 complete waves fit in a length of 4 m4 \text{ m}. Therefore, 5λ=4 m    λ=45=0.8 m5\lambda = 4 \text{ m} \implies \lambda = \frac{4}{5} = 0.8 \text{ m}.
  3. Calculate the Wave Number (kk): The wave number is k=2πλk = \frac{2\pi}{\lambda} . k=2π0.8=2.5π2.5×3.14=7.85 rad/mk = \frac{2\pi}{0.8} = 2.5\pi \approx 2.5 \times 3.14 = 7.85 \text{ rad/m}
  4. Calculate the Angular Frequency (ω\omega): The wave speed is v=ωkv = \frac{\omega}{k}, so ω=vk\omega = v \cdot k . ω=128×7.85=1004.81005 rad/s\omega = 128 \times 7.85 = 1004.8 \approx 1005 \text{ rad/s}
  5. Determine the Wave Equation: The general equation for a wave travelling in the positive x-direction is y=Asin(kxωt)y = A\sin(kx - \omega t) or y=Asin(ωtkx)y = A\sin(\omega t - kx) . Looking at the options, we use the form y=Asin(kxωt)y = A\sin(kx - \omega t). Substituting the values, we get: y=0.02sin(7.85x1005t)y = 0.02 \sin(7.85x - 1005t)

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from WAVE. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSWAVEstringamplitudetravelsdirectioncomplete

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