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JEE Main 2014 (19 Apr, Shift 1) · Stationary Waves & Vibrating Strings

Stationary Waves & Vibrating Strings question from JEE Main 2014 (19 Apr, Shift 1)

Q102JEE Main 2014 · 19 APR · SHIFT 1Medium

Stationary Waves & Vibrating Strings

The total length of a sonometer wire between fixed ends is 110 cm. Two bridges are placed to divide the length of wire in ratio 6: 3: 2. The tension in the wire is 400 N and the mass per unit length is 0.01 kg/m. What is the minimum common frequency with which three parts can vibrate?

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Answer: (b)

  1. Lengths: 60,30,20 cm60, 30, 20\text{ cm}. Wave speed v=T/μ=400/0.01=200 m/sv=\sqrt{T/\mu}=\sqrt{400/0.01}=200\text{ m/s}.
  2. Fundamentals f=v2lf=\frac{v}{2l}: 2001.2=166.7\frac{200}{1.2}=166.7, 2000.6=333.3\frac{200}{0.6}=333.3, 2000.4=500 Hz\frac{200}{0.4}=500\text{ Hz}.
  3. Common frequency must be a whole multiple of each: LCM of 5003,10003,500\frac{500}{3}, \frac{1000}{3}, 500 is 1000 Hz1000\text{ Hz}.
  4. So the answer is (b) 1000 Hz.
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