Question Detail

PHY 104 Wave and sound Objective Question

Question

Following from the previous question (Q6), write the equation for the displacement y(x,t) of the string as a function of position x and time t, assuming it's a standing wave with maximum displacement at the antinodes (0.5 mm).
Options
A y(x,t) = 0.0005 sin(9π/5 x) cos(450πt)
B y(x,t) = 0.0005 sin(18π/5 x) cos(900πt)
Correct Answer
C y(x,t) = 0.0005 cos(18π/5 x) sin(900πt)
D y(x,t) = 0.0005 cos(9π/5 x) cos(450πt)
Correct Answer

Option B is the correct answer.

Detailed Explanation

The general equation for a standing wave on a string fixed at both ends is y(x,t) = A_stand sin(kx) cos(ωt) (or sin(ωt)).From the previous problem: A_stand = 0.5 mm = 5.0 × 10⁻⁴ m.Wavelength λ = 5/9 m, so k = 2π/λ = 2π / (5/9) = 18π/5 rad/m.Frequency f = 450 Hz, so ω = 2πf = 2π * 450 = 900π rad/s.Substituting these values gives: y(x,t) = (5.0 × 10⁻⁴ m) sin((18π/5)x) cos(900πt).(Note: The choice between sin(ωt) or cos(ωt) depends on the exact initial phase, but cos(ωt) is a common form if the wave is at maximum displacement at t=0.)

Hint

Recall the general form of a standing wave equation. Calculate the wave number (k) and angular frequency (ω) using the wavelength and frequency, and use the given amplitude.

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