Q.

A horizontal stretched string, fixed at two ends, is vibrating in its fifth harmonic according to the equation,

 y(x,t)=(0.01 m)sin[(62.8 m-1)x]cos[(628 s-1)t].  Assuming π=3.14, the correct statement(s) is (are)                   [2013]

1 The number of nodes is 5  
2 The length of the string is 0.25 m  
3 The maximum displacement of the midpoint of the string, from its equilibrium position is 0.01 m  
4 The fundamental frequency is 100 Hz  

Ans.

(2, 3)

y=[0.01sin(62.8x)]cos(628t)    [Given]

From the given equation, k=2πλ=62.8

  λ=2π62.8=0.1 m

Length of string, l=5×λ2=5×120=0.25 m

The midpoint M is an antinode and has the maximum displacement =0.01 m

The fundamental frequency, ν=v2l=ω/k2l

=6282×0.25×62.8=20 Hz