The speed of a longitudinal wave in a metallic bar is 400 ~m / s. If the density and Young's modulus of the bar material are increased by 0.5 % and 1…
JEE Main 2026 — Physics Waves & Oscillations
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The speed of a longitudinal wave in a metallic bar is 400m/s. If the density and Young's modulus of the bar material are increased by 0.5% and 1%, respectively then the speed of the wave is changed approximately to ____m/s.
Official previous-year question
Held on 28 Jan 2026 · Verified 6 Jul 2026.
Options
A
398
B
401
C
399
D
402
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Solution
The speed of a longitudinal wave in a solid is given by v=ρY where Y is Young's modulus and ρ is density.
Initial condition: v0=ρY=400 m/s
After changes: ρ′=1.005ρ (0.5% increase) and Y′=1.01Y (1% increase)
New speed: v′=ρ′Y′=1.005ρ1.01Y=1.0051.01⋅ρY
v0v′=1.0051.01=1.00498...≈1.00249
v′=400×1.00249≈401 m/s
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