question_answer

A wire is 4 m long and has a mass 0.2 kg. The wire is kept horizontally. A transverse pulse is generated by plucking one end of the taut (tight) wire. The pulse makes four trips back and forth along the cord in 0.8 sec. The tension is the cord will be-

A) 80 N                            

B) 160 N

C) 240 N               

D) 320 N

Correct Answer: A

Solution :

4 trips means 32 m \[t=\frac{d}{v}\,\,\,\Rightarrow \,\,v=\frac{d}{t}\,\,=\,\,\frac{32}{0.8}\,\,=\,\,40\,m/s\] \[v=\sqrt{\frac{T}{\mu }}\] \[\Rightarrow \,\,\,T\,\,=\,\,\mu {{v}^{2}}\] \[T=\frac{0.2}{4}\,\times {{(40)}^{2}}\,\,=\,\,\frac{2\times 16\times 10}{4}\] \[T\,\,=\,\,80\,N\]