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NEET 2016
Exam
NEET
Year
2016
Subject
Physics
Chapter
Waves and Sound

NEET 2016 · Physics · Waves and Sound

A uniform rope of length L and mass m _ 1 , hangs vertically from a...

A uniform rope of length LL and mass m1{m}_{1}, hangs vertically from a rigid support. A block of mass m2{m}_{2} is attached to the free end of the rope. A transverse pulse of wavelength λ1{\lambda}_{1} is produced at the lower end of the rope. The wavelength of the pulse when it reaches the top of the rope is λ2{\lambda}_{2}. The ratio λ2λ1\dfrac{{\lambda}_{2}}{{\lambda}_{1}} is:A uniform rope of length L and mass m _ 1 , hangs vertically from a rigid support. A block of mass m _ 2 is attached to

Options

  1. Am2m1\sqrt{\dfrac{{m}_{2}}{{m}_{1}}}
  2. Bm1+m2m2\sqrt{\dfrac{{m}_{1} + {m}_{2}}{{m}_{2}}}
  3. Cm1m2\sqrt{\dfrac{{m}_{1}}{{m}_{2}}}
  4. Dm1+m2m1\sqrt{\dfrac{{m}_{1} + {m}_{2}}{{m}_{1}}}

Correct answer

B. m1+m2m2\sqrt{\dfrac{{m}_{1} + {m}_{2}}{{m}_{2}}}

Step-by-step solution

The situation in the rope is given below,

A uniform rope of length L and mass m _ 1 , hangs vertically from a rigid support. A block of mass m _ 2 is attached to

The velocity of the wave at the bottom of the rope is given by,

v=Tμv = \sqrt{\dfrac{T}{\mu}}; where TT is tension and μ\mu is linear mass density of the string.

v1=m2gLm1{v}_{1} = \sqrt{\dfrac{{m}_{2}gL}{{m}_{1}}}

Hence, the wavelength for frequency ff will be,

λ1=v1f=1fm2gLm2{\lambda}_{1} = \dfrac{{v}_{1}}{f} = \dfrac{1}{f}\sqrt{\dfrac{{m}_{2}gL}{{m}_{2}}}

Similarly, at top the velocity will be,

v1=(m1+m2)gLm1{v}_{1} = \sqrt{\dfrac{( {m}_{1} + {m}_{2} )gL}{{m}_{1}}}

And, the wavelength will be,

λ2=1f(m1+m2)gLm1{\lambda}_{2} = \dfrac{1}{f}\sqrt{\dfrac{( {m}_{1} + {m}_{2} )gL}{{m}_{1}}}

Hence, the ratio of both wavelengths will be,

λ2λ1=m1+m2m2\dfrac{{\lambda}_{2}}{{\lambda}_{1}} = \sqrt{\dfrac{{m}_{1} + {m}_{2}}{{m}_{2}}}.

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