A) 14 rpm
B) 10 rpm
C) 2.25 rpm
D) 7 rpm
Correct Answer: D
Solution :
Tension in the string \[T=m{{\omega }^{2}}r=4{{\pi }^{2}}{{n}^{2}}mr\] \ \[T\propto {{n}^{2}}\] Þ \[\frac{{{n}_{2}}}{{{n}_{1}}}=\sqrt{\frac{{{T}_{2}}}{{{T}_{1}}}}\] Þ \[{{n}_{2}}=5\sqrt{\frac{2T}{T}}=7\,rpm\]
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