A) 4s
B) 2s
C) 8s
D) 1 s
Correct Answer: B
Solution :
The moment of inertia of needle when it cuts into two halves by a plane normal to magnetic axis of the needle. \[I\,=\frac{1}{12}\,\left( \frac{m}{2} \right)\,{{\left( \frac{l}{2} \right)}^{2}}\,\] or \[g\propto \frac{1}{{{(R+h)}^{2}}}\] Also, \[\therefore \] \[g=g\frac{{{R}^{2}}}{{{(R+h)}^{2}}}=\frac{9.8\times {{(6400)}^{2}}}{{{(6400+480)}^{2}}}\] The period of vibration \[=8.4m/{{s}^{2}}\] \[\left( P+\frac{{{\mu }^{2}}a}{{{V}^{2}}} \right)(V-\mu b)=\mu RT\]
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